Insulated composite heat shield for vehicle exhaust system

An exhaust component assembly includes a heat shield formed from a composite material and a mounting structure that attaches the heat shield to an outer housing of an exhaust component. The mounting structure comprises an insulator located between an outer surface of the outer housing an inner surface of the heat shield. A method of assembling the composite heat shield to the outer housing of the exhaust component assembly is also disclosed.

BACKGROUND OF THE INVENTION

Vehicles include an exhaust system that transports exhaust gas generated by a combustion engine to a location on the vehicle where the heated exhaust gas can be emitted safely. Exhaust systems can include various combinations of the following components: pipes, tubes, resonators, converters, catalysts, filters, mixers, mufflers, etc. The entire exhaust system becomes very hot after a short period of operation due to the high temperatures generated during the combustion processes that produce the exhaust gas. As such, one or more of the components often utilize an outer heat shield to reduce the overall exposed external surface temperature of the components.

A typical heat shield is a thin sheet of metal that is stamped or otherwise formed to conform generally to the shape of the component to which the heat shield is to be attached, such as a muffler for example. The heat shield may be formed with legs or other structures that provide areas for attaching the heat shield to the muffler. Remaining portions of the heat shield are spaced along an outer surface of the muffler to insulate external areas of the shield from the muffler. The heat shield is typically secured to the muffler by welding; however, other attachment methods, such as straps, rivets, etc. have been used additionally or alternatively.

In certain environments it is important to shield as much of a hot exhaust component as possible. For example, some specifications may require as high as 99% of the outer surface of the component to be less than a specified temperature. This requirement can be difficult to achieve with larger components and with components having complex shapes. Further, the various attachment structures used to attach the heat shield to the component provide direct conduits for transferring heat to the heat shield, which can make it difficult to maintain a desired low outer surface temperature.

SUMMARY OF THE INVENTION

According to one exemplary embodiment, an exhaust component assembly includes a heat shield formed from a composite material and a mounting structure that attaches the heat shield to an outer housing of an exhaust component. The mounting structure comprises an insulator located between an outer surface of the outer housing an inner surface of the heat shield.

In another embodiment according to the previous embodiment, the exhaust component defines a center axis and the heat shield has an outer surface spaced radially outward of the inner surface of the heat shield. In one example, an additional layer of insulating material is attached to one or both of the inner and outer surfaces of the heat shield.

In another embodiment according to any of the previous embodiments, the heat shield includes at least one internal cavity encapsulated within the heat shield.

In another embodiment according to any of the previous embodiments, the insulator comprises a primary insulator and at least one secondary insulator positioned adjacent the primary insulator.

In another exemplary embodiment, a method of assembling a heat shield to an outer housing of an exhaust component assembly includes providing a heat shield made from a composite material, and supporting the heat shield on a mounting structure configured to attach the heat shield to an outer housing of an exhaust component, wherein the mounting structure comprises an insulator located between an outer surface of the outer housing an inner surface of the heat shield.

In another embodiment according to any of the previous embodiments, the heat shield is compressed against the outer housing.

In another embodiment according to any of the previous embodiments, the heat shield is formed by thermo-forming, molding, or additive manufacturing.

In another embodiment according to any of the previous embodiments, one or more protrusions are integrally formed with the heat shield to extend out from an outer surface of the heat shield.

DETAILED DESCRIPTION

FIG. 1shows a vehicle exhaust system10that conducts hot exhaust gases generated by an engine12through various upstream exhaust components14to reduce emission and control noise as known. Downstream from the engine are various upstream exhaust components14that can include one or more of the following in any combination: pipes, filters, valves, catalysts, mufflers, etc. In one example configuration, the various upstream exhaust components14direct exhaust gases into a diesel oxidation catalyst (DOC)16having an inlet18and an outlet20. Downstream of the DOC16there may be a diesel particulate filter (DPF)21that is used to remove contaminants from the exhaust gas as known.

Downstream of the DOC16and optional DPF21is a selective catalytic reduction (SCR) catalyst22having an inlet24and an outlet26. The outlet26communicates exhaust gases to downstream exhaust components28. Optionally, component22can comprise a catalyst that is configured to perform a selective catalytic reduction function and a particulate filter function. The various downstream exhaust components28can include one or more of the following in any combination: pipes, filters, valves, catalysts, mufflers, etc. The components shown inFIG. 1can be mounted in various different configurations and combinations dependent upon vehicle application and available packaging space.

In one example configuration, a mixer30is positioned downstream from the outlet20of the DOC16or DPF21and upstream of the inlet24of the SCR catalyst22. The mixer30is used to generate a swirling or rotary motion of the exhaust gas. Any type of mixing element can be used, such as that set forth in US 2012/0216513 for example, which is assigned to the assignee of the present invention and is herein incorporated by reference. An injection system32is used to inject a reducing agent, such as a solution of urea and water for example, into the exhaust gas stream upstream from the SCR catalyst22such that the mixer30can mix the urea and exhaust gas thoroughly together. The injection system32includes a fluid supply34, a doser36, and a controller38that controls injection of the urea as known. Such a system in combination with a mixer is disclosed in U.S. application Ser. Nos. 14/737,533 and 14/737,546 for example, which are assigned to the assignee of the present invention and are herein incorporated by reference.

In one example, the mixer30includes a heat shield40that is mounted to an outer housing42of the mixer30using a unique low conductive support mount configuration43. The low conductive support mount43is configured such that the heat internally within the exhaust component is maintained at the desired temperature levels while the outer surface of the component is maintained at much cooler surface temperatures. In one example embodiment shown inFIG. 2, the low conductive support mount43comprises a primary insulator44that is located between an outer surface46of the outer housing42and an inner surface48of the heat shield40, and at least one secondary insulator50positioned adjacent the primary insulator44. The heat shield40includes openings as needed, such as for example, an opening40afor a mount structure as for the doser36as shown inFIG. 2. The combination of primary44and secondary50insulators is used to insulate the heat shield40from the outer housing42by removing direct contact (conduction path) between the housing42and heat shield40, while also maintaining a generally constant gap between them.

FIG. 3shows a section view of the mixer30which includes inlet52and outlet54baffles that are surrounded by a mixer body56. The body56is mounted within the outer housing42of the mixer30. In this example, the primary insulator44comprises an insulation mat58that surrounds the outer surface46of the housing42. The secondary insulators50comprise one or more bands or rings60that are used in combination with the insulation mat58to mount the heat shield40on the housing42. In the example shown, one ring60is placed at one edge of the mat58and another ring60is placed at an opposite edge of the mat58. The heat shield40is placed over outer surfaces of the mat58and rings60and is then compressed radially inward to compress the mat58against the housing42. One or more additional attachment structures such as straps or clamps62, for example, are then used to hold the mat58in compression.

FIG. 4shows an example where the mat58in an uncompressed state andFIG. 3shows an example of the mat58being in a compressed state where the heat shield40is secured using clamps62. While clamps are shown inFIG. 3, it should be understood that other attachment structures could be used to hold the mat58and heat shield in compression against the outer housing42.

The heat shield40is made from a non-metallic material such as composite or plastic material, for example. The rings60protect the mat58, provide structural support for the heat shield40, and resist movement of the heat shield40during vehicle operation. The rings60can comprise a band of fiber mat or a fibrous material such as rope, for example. The rings60preferably comprise bands of a high-stiffness mat, a rope of braided rope material, a rope of braided wire material, a rope that includes glass fibers, or other similar materials. The rings60can be comprised of a compressible or non-compressive material. In one example, the mat58has a first stiffness and the rings60have a second stiffness that is greater than the first stiffness.

In the example shown inFIG. 3-4, both the mat58and rings60are compressed by the heat shield40against the outer housing42.FIG. 4shows the mat58having an initial first thickness T1and the rings60having an initial second thickness T2in the uncompressed state. The heat shield40is then placed around the mat58and rings60and is compressed in a radially inward direction. This causes the mat58to be compressed to a final thickness T3that is less than the initial first thickness T1, and the rings60to be compressed to a final thickness T4that is less than the initial second thickness T2(FIG. 3). The clamps62are then secured over opposing edges of the heat shield40at radially outward positions that overlap each of the rings60such that in this final installation position, the heat shield40is held in compression against the housing42. Distal ends68of the heat shield40remained spaced apart from the housing42when compressed.

FIG. 5shows an example where clamps are not used to hold the heat shield40in compression. Instead, edge portions66of the heat shield40are formed to extend around the rings60. In one example, the edge portions66are formed as circumferential indentations. Optionally, the indentations could be replaced by barbs to hold the rings60in place. These edge portions66can be pre-formed and pressed against the mat58and rings60or the edge portions66can be plastically, i.e. permanently, deformed around the rings60during installation to hold the mat58and heat shield58in compression against the housing42. The edge portions66can be roll-formed, stamped, molded, welded, cast, etc. An indented area67between an edge of the mat58and the curved indentation helps locate and define a boundary between the ring60and mat58. The edge portions66help prevent movement of the heat shield40once the shield is compressed. The edge portions66are deformed such that the distal ends68of the edge portions66remain spaced apart from the housing42such that there is no direct heat transfer contact.

In this example configuration, the mat58provides structural support to attach the heat shield40to the housing42without the use of any other attachment structures. As portions of the heat shield40are compressed around the mat58and against the housing42, the portions are subsequently attached to each other to hold the mat58and shield40in compression against the housing42. This will be discussed in greater detail below.

In one example, the rings60can comprise a high-stiffness, non-compressive mat that is placed on opposing sides70of the mat58. The heat shield40is compressed against the mat58causing the mat58to decrease in thickness from the initial first thickness to a smaller final second thickness while the non-compressive mat at each of the opposing sides70remains at substantially the same thickness. Clamps62or other attachment structures can then be used to hold the heat shield40in compression against the housing42.

The configurations shown inFIGS. 2-5each include a central insulating mat58and two pieces of material such as braided rope, braided wire, or high-stiffness mat that are placed at opposing edges70of the mat58. The two pieces of material comprise the bands or rings60, and in one example, these rings60are in direct abutting contact with the edges70of the mat, the outer surface46of the housing42and the inner surface48of the heat shield40. Further, in each of the examples, once the heat shield40is held in compression against the housing42, the distal edges68of the heat shield40remain spaced from the outer surface46of the housing by a gap72(FIG. 5).

FIG. 6shows one example of a heat shield40that is formed from a composite material. The composite material can comprise a fiber-reinforced polymer or plastic material, a multi-layer composite material, etc. The heat shield40can be a solid part, a part made from multiple layers, or can comprises a honeycomb structure, for example.

The heat shield40can be formed as one or more composite shield portions80(only one is shown inFIG. 6) that are configured to surround the outer housing42which defines a central axis A. The portions80can be formed using processes such as molding, thermoforming, or additive manufacturing for example.

FIG. 6shows one example of a C-shaped composite shield portion80. The composite shield portion80includes an inner surface86and an outer surface88spaced radially outward of the inner surface86. The distance between the inner86and outer88surfaces defines a thickness90of the composite shield portion80. In certain locations, the composite shield portion80is solid throughout the thickness90. However, the composite shield portion80may include one or more discrete internal cavities92that are encapsulated within the composite shield portion80.

In one example, one or more of the cavities92comprises an internal air pocket92athat is used to further enhance the insulating properties and/or to lighten the heat shield40. In another example, one or more of the cavities92bis filled with a material to further enhance the insulating properties and/or to stiffen and reinforce the heat shield40. The material filling the cavities92bcan also be a composite material, or can be a structural material such as steel, wire mesh, etc. The additional material filling the cavities92can be included by over-molding, insert molding, additive manufacturing, or other similar processes.

In one example, the composite shield portion80can optionally include an additional layer of insulating material94attached to one or both of the inner86and outer88surfaces of the composite shield portion80. The additional layer of insulating material94can comprise a wire mesh, a metal sheet, a foil sheet, etc. for example. The additional layer of insulating material94can cover an entire surface of the composite shield portion80or can cover only certain locations on the composite shield portion80. For example, the additional layer of insulating material94can be added at identified hot spot locations96which are determined based on component type and application.

In one example shown inFIG. 7, the composite shield portion80can also optionally include one or more ribs or protrusions98that extend outwardly from the outer surface88of the composite shield portion80. Certain protrusions98, such as ribs for example, can further facilitate the reduction of heat transfer while other protrusions can be used as standoffs or mounting posts to facilitate attachment of other components such as cables, wiring, sensors, etc. to the mixer30. In one example, the protrusions98are integrally formed as one-piece with the composite shield portion80to provide a unitary, monolithic structure.

In one example, the heat shield40can include multiple layers such as an outer shield portion40aand an inner shield portion40b. The protrusions98in this example are formed in the outer shield portion40a. Further, this type of shield40can be used in any of the disclosed examples. Also, the mat58may include one or more encapsulated cavities100(FIG. 7) that can be empty air pockets or filled with material such as microporous material, for example. This type of mat58could also be used in any of the disclosed examples.

FIGS. 8A-8Dshow one example of attaching shield portions together80. One shield portion80includes one or more fasteners102and the other shield portion80includes corresponding openings108to receive the fasteners102. In one example, the fasteners extend to a distal gripping finger104spaced from the shield portion80to form a groove106that receives a corresponding portion of the mating shield portion80.

FIG. 9shows one example of shielding as used around bosses110that are associated with the housing42. Recessed areas112are formed around the bosses110. These areas112can be empty or further filled with insulating material as needed.

In one example, a support layer78(FIG. 4) for the mat58and/or rings60is applied to the outer surface46of the housing42. In one example, the support layer78comprises a layer of adhesive material that holds the mat58and/or rings60in place until an attachment structure such as clamps62, straps or bolts, for example, are installed to hold the heat shield40in compression against the housing42. Optionally, the rings60and mat58can be attached to the support layer78to form an assembly that is then wrapped around the housing42as a unit. Use of the support layer78provides the benefit of a simple and effective installation of the heat shield40.

In each of the examples, the rings60can be sealed or unsealed structures depending upon the desired specifications. Ideally, the rings60should provide structural support, insulation, and sealing to the heat shield40and component assembly. When the rings60are comprised of a rope made of braided fibers, the rope can be treated with a coating, for example, to be waterproof and to act as a seal. When the rings60are comprised of a band or ring made from a mat that is sensitive to water, an additional seal might be needed. This seal can be made of insulating foam or be a gasket made with heat-insulating material, such as mica, for example.

In one example, the central mat58and rings60can be manufactured as one assembly for easier installation. Further, the cross-sectional shape of the rings60can be circular, oval, square, rectangular, etc.

In one example, the rings60comprise two square or rectangular section braided wire bands that are 10-20 mm in width and which can withstand outer surface temperatures of 500-600 degrees Celsius. The polygonal section braided wire bands should have a high density/low compressibility such that when the bands are compressed they are approximately 7 mm thick in a radial direction. The ring material should comprise a material with very low thermal conductivity, such as less than 0.1 W/m·K at 600 degrees Celsius, for example.

In one example, the mat58comprises a fiber mat that is 10-15 mm thick when uncompressed (T1), and is approximately 7 mm when compressed (T3). As discussed above, a layer or sheet of adhesive can be applied to the housing42as the support layer78, and the mat58and bands60can then be attached as a unit or individually in a direct manner to the adhesive. Optionally, the mat58and bands60can be attached to the adhesive sheet prior to attachment to the housing42with the components then being wrapped as an assembly about the housing42. Once the mat58and bands60are in place on the housing, the heat shield40is installed such that the bands and mat are compressed.

FIGS. 2-5show an example where the insulating mat58is comprised of a single layer of material. The mat could also be formed from a plurality of layers of material. Examples of multi-layer mats can be found in co-pending application 16/085,232 file on Sep. 14, 2018, which is a national phase of PCT/US17/23713 filed on Mar. 23, 2017, which is assigned to the assignee of the subject application and is hereby incorporated by reference.

FIG. 10shows one example method of assembly that comprises a tourniquet process. In this example, the method includes a step of forming400the heat shield portions80as described above, for example, and then includes the step of wrapping402the portions80around the internal insulating assembly44,50and mixer housing42. The portions80are then tightened404around the internal insulating assembly and are held at a location where the portions80overlap with each other as shown inFIG. 7, for example. The portions80are tightened until a desired level of compressive force is achieved for the subject component application and are then connected to each other406at the overlap to be sealed via welding or brazing, for example, or by fastening the fasteners102in the openings108. Other possible types of attachment of the portions80together include strapping, clamping, clipping, brazening or welding the portions80together. It should be understood that this is just one example of an assembly method and that other methods of compressing the internal insulating assembly44,50can be used.

Once the portions80are attached to each other, the whole mixer assembly30is held together in compression. If the compressive force is not sufficient to maintain the assembly in place due to axial loading, some features can be added to the housing42to help keeping the assembly in place, such as mechanical stops for example. If the compressive force is not sufficient to maintain the assembly in place due to radial loading, additional mount structures such as straps, fasteners, or clamps62for example, can be installed on the heat shield40.

It should be understood that while the heat shield40and unique low conductive support mount configuration43are shown in this example as being mounted to a mixer30, the subject heat shield and associated mounting configuration can be used with any other vehicle exhaust system component as needed. For example, the subject heat shield mounting configurations could be used with mufflers, DOCs, DPFs, tailpipes, etc. Further, the subject heat shield mounting configurations could be used with larger box-shaped system components that include flat sides, where the heatshield would be pre-formed to get in compression.

The subject invention utilizes a unique mounting structure43for a heat shield40made from a composite material, where the mounting structure43comprises an insulator that supports the composite heat shield. An exemplary insulator comprises a primary insulator44in combination with one or more secondary insulators50as described above. The primary insulators44are used as structural support to attach the heat shield40to the outer housing42. The secondary insulators50are configured to hold the heat shield40and primary insulator44in place relative to the outer housing42. The secondary insulators comprise pieces of material, bands, or rings60that provide for a higher stiffness area than that of the primary insulator44.

As discussed above, temperatures at the outer surface46of the housing42can be as high as 600 degrees Celsius. In each of the disclosed examples, the composite heat shield and mounting structure cooperate with each other to maintain as high as 90-99% of an outer surface of the heat shield at a temperature that can be as low as approximately 300 degrees Celsius or even as low as 200 degrees Celsius, for example, which is a significant improvement over existing heat shield configurations.