Patent Publication Number: US-6209319-B1

Title: Pipe assembly having inner and outer pipes

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to pipes that convey exhaust gases from an internal combustion engine, and more particularly to a pipe assembly for conveying exhaust gases that includes inner and outer pipes. 
     2. Description of the Related Art 
     Some existing exhaust manifold designs include a set of single-walled pipes emanating from an internal combustion engine and connected to downstream pipes. Significant noise is generated, however, when exhaust gases are conveyed from an internal combustion engine through a set of single-walled pipes emanating from the engine. 
     Single-walled pipes are susceptible to thermodynamic heat loss, which impedes operation of a catalytic converter, caused by the ambient atmosphere surrounding the single-walled pipe. Single-walled pipes are also easily damaged by impact, dirt, debris and corrosive substances. Because single-walled pipes suffer from the aforementioned and other shortcomings, there have been attempts to convey exhaust gases through double-walled pipes. 
     For example, in U.S. Pat. No. 4,022,019 to Garcea, two outer corrugated tubes are slipped over an inner smooth tube. The outer corrugated tubes insulate the inner tube, reducing heat transfer toward the outside atmosphere. 
     In U.S. Pat. No. 5,390,494 to Clegg, an inner pipe is surrounded by a thicker outer pipe. Corrugations in the inner pipe provide support during bending and reduce heat dissipation to the surrounding areas. 
     There continues to be a need, however, for new structural arrangements that reduce engine noise emitted by exhaust gas conduits while preventing heat dissipation from the exhaust gas conduits. 
     SUMMARY OF THE INVENTION 
     According to an exemplary embodiment of the invention, a pipe assembly for conveying exhaust gases includes an inner pipe and an outer pipe disposed around the inner pipe. The outer pipe includes an outer layer and an inner layer attached, such as by lamination, to the outer layer. Noise emitted from the pipe assembly is reduced by laminating the outer layer and the inner layer and selecting the thickness of the outer layer to be twice the thickness of the inner layer. A set of such pipe assemblies can be deployed in pairs in an exhaust manifold. When paired, the planar side wall of one of the pipe assemblies is in confronting relation with the planar side wall of the other pipe assembly of the pair. 
     Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan sectional view of a pipe assembly in accordance with the principles of the invention; 
     FIG. 2 is a cross-sectional view taken along the line A—A in FIG. 1; 
     FIG. 3 is a cross-sectional view taken along the line B—B in FIG. 1; 
     FIG. 4 is a cross-sectional view taken along the line C—C in FIG. 1; 
     FIG. 5 is a cross-sectional view taken along the line D—D in FIG. 1; and 
     FIG. 6 is a perspective view of an exhaust manifold in accordance with the principles of the invention. 
    
    
     DETAILED DESCRIPTION 
     As shown in the drawings for purposes of illustration, the invention is embodied in a pipe assembly that includes an inner pipe and an outer laminated pipe disposed around the inner pipe for use in conveying exhaust gases from an internal combustion engine. The outer pipe is formed from two or more laminated layers. 
     The pipe assembly has an upstream inlet portion connectable, for example, to an exhaust port of a cylinder of an internal combustion engine. A downstream outlet portion of the pipe assembly is connectable to one or more exhaust pipes. 
     The outer pipe surrounds the inner pipe to protect the inner pipe, and muffle the inner pipe, while the inner pipe provides support for the outer pipe, either consistently contacting the outer pipe at the upstream inlet portion, or contacting the outer pipe at three areas spaced from each other on the outer pipe at the downstream outlet portion. The three contacting areas at the downstream outlet portion create an air-filled space at least partially separating the inner pipe and the outer laminated pipe. The air-filled space insulates the inner pipe so that exhaust gas moving through the inner pipe does not cool significantly as a result of heat dissipating by conduction or convection to the outer pipe. 
     Because the exhaust gases remain hot in the pipe assembly, they are hotter at a catalytic converter disposed downstream of the pipe assembly. Hot exhaust gases achieve a faster light-off of the catalytic converter (i.e., attaining a sufficiently hot working temperature range) so that the catalytic converter quickly works to remove hydrocarbon and other harmful components contained in the exhaust gases. The distance separating the inner pipe and the outer laminated pipe can be adjusted to vary along the length of the pipe assembly. Such separation distance is greatest throughout a portion of the pipe assembly intermediate the upstream inlet portion and the downstream outlet portion, where thermal insulation of the inner pipe is greatest. These and other features of the preferred embodiments of the invention will become more fully apparent with reference to the drawings. 
     FIG. 1 shows a plan sectional view of a pipe assembly  10  having an inner pipe  12  and an outer pipe  14  in accordance with the principles of the invention. Referring to FIG. 1, the pipe assembly  10  generally has a curvilinear shape which is based on the need to connect a particular cylinder at one position and orientation to an exhaust pipe at another position and orientation. The pipe assembly  10  shown in FIG. 1 includes an upstream inlet portion  16 , a downstream outlet portion  18  and a portion  20  intermediate the upstream inlet portion and the downstream outlet portion. 
     The upstream inlet portion  16  of the pipe assembly has a “race-track” cross-sectional configuration, as illustrated in and subsequently described with reference to FIG. 2, that can be registered with, or friction-fit within, a similarly shaped inlet opening defined by an inlet flange mountable on an internal combustion engine. At the upstream inlet portion  16  of the pipe assembly, the inner pipe  12  is welded to uniformly contact the surrounding outer pipe  14 . Such “race-track” cross-sectional configuration is the shape presented by a rectangle that has each of its two short sides replaced by the arc of a semi-circle (or another kind of curved arc). A “race-track” cross-sectional configuration also includes an oval shape, an elliptical shape, or an oblong shape. 
     At a first lengthwise position intermediate the upstream inlet portion  16  and the downstream outlet portion  18 , the pipe assembly  10  presents a substantially circular cross-sectional configuration, as illustrated in and subsequently described with reference to FIG.  3 . Along the length of the pipe assembly, within such first lengthwise position of such intermediate portion  20 , the inner pipe  12  is separated from the outer pipe  14  to reduce heat conduction and/or convection to the outer pipe. Further downstream, at a second lengthwise position intermediate the upstream inlet portion  16  and the downstream outlet portion  18 , the cross-sectional configuration of the pipe assembly  10  changes to a race-track cross-sectional configuration, as illustrated in and subsequently described with reference to FIG. 4, at which point the outer pipe  14  and the inner pipe  12  remain separated by a preselected distance to reduce heat dissipation to the outer pipe. The separation distance can be adjusted based on thermal insulation and/or noise elimination requirements. 
     The downstream outlet portion  18  of the pipe assembly  10  has a substantially “D-shaped” cross-sectional configuration (i.e., the shape presented by a straight line connecting the ends of the arc of a semi-circle or another curved shape), as illustrated in and subsequently described with reference to FIG.  5 . Both the outer laminated pipe  14 , and the inner pipe  12  disposed within the outer laminated pipe  14 , present such a D-shaped cross-sectional configuration at the downstream outlet portion  18  of the pipe assembly  10 . 
     According to the principles of the invention, a pipe assembly can be paired with another pipe assembly in an exhaust manifold by attaching (e.g., by welding) the downstream outlet portions of the pipe assemblies, as illustrated in FIG.  6 . When two pipe assemblies are attached at their downstream outlet portions, the pipe members present a combined cross-sectional configuration that will fit into an outlet opening that has a substantially circular cross-sectional configuration. The outer laminated pipe  14  of the pipe assembly presents a substantially planar side wall along the downstream outlet portion  18 . In combination, the planar side wall of one outer laminated pipe is in confronting relation with the planar side wall of the other outer laminated pipe of the pair. 
     According to the specific embodiment illustrated in FIG. 1, the outer pipe of the pipe assembly is formed of an inner layer  22  and an outer layer  24  to reduce noise emitted from the pipe assembly  10  in accordance with the principles of the invention. The inner layer  22  is preferably laminated to the outer layer  24 . The respective thicknesses of the inner layer  22  and the outer layer  24  are selected in relation to and based upon each other to achieve optimum noise reduction. The thickness of the outer layer  24  of the outer pipe  14  is preferably selected to be double that of the inner layer  22  of the outer pipe. Experimental testing has shown that this thickness relationship between the inner and outer layers  22 ,  24  of the outer pipe  14  produces the optimum reduction of noise. 
     In the preferred embodiment of the invention, the pipes are made from austenitic stainless steel. However, any other suitable material such as just stainless steel or steel can also be used. The thickness of the outer layer  24  is substantially equal to 0.8 mm and the thickness of the inner layer  22  is substantially equal to 0.4 mm. The inner pipe  12  has a thickness substantially equal to 0.6 mm. It has been found that this thickness relationship between the inner layer  22  and the outer layer  24  provides the best noise reduction. 
     Vibrations from the operating engine, along with continual heating and cooling, can cause engine exhaust gas conduits to crack. Accordingly, the invention contemplates that other thickness relationships between the inner layer  22  of the outer pipe and the outer layer  24  of the outer pipe can be employed, and that a relatively thicker inner layer  22  can be used so that possibly vibrations and other effects of engine operation do not cause the thin inner layer  22  of the outer pipe to crack from the vibratory stresses. 
     For example, in another specific embodiment, the inner pipe  12  can have a thickness of 0.6 mm, the inner layer  22  of the outer pipe can have a thickness of 0.6 mm and the outer layer  24  can have a thickness of 0.8 mm. The 0.6 mm-thick inner layer  22  in this specific embodiment of the invention is probably less prone to cracking and can give additional endurance to the pipe assembly. 
     FIG. 2 is a cross-sectional view of the upstream inlet portion of the pipe assembly  10  taken along the line A—A in FIG.  1 . With reference to FIG. 2, the inner pipe  12  and the outer laminated pipe  14  are welded to each other. The inner pipe  12  and the outer laminated pipe  14  each have a race-track cross-sectional configuration. As shown in FIG. 2, the inner pipe  12  and the outer laminated pipe  14  are in substantially contacting relationship at the upstream inlet portion  16  (FIG. 1) for mutual support. 
     FIG. 3 is a cross-sectional view of the pipe assembly  10  taken along the line B—B in FIG. 1, at a lengthwise position further downstream along the length of the pipe assembly from the upstream inlet portion illustrated in FIG.  2 . With reference to FIG. 3, the inner pipe  12  and the outer pipe  14  are shown in substantially spaced relation to reduce thermal dissipation so that quicker light-off of a catalytic converter can be accomplished. At the lengthwise position depicted in FIG. 3, the inner pipe  12  and the outer laminated pipe  14  each present a substantially circular cross-sectional configuration and are spaced from each other by a predetermined separation distance, which is measured radially outward from the outer surface of the inner pipe  12  to the inner surface of the inner layer  22 . 
     FIG. 4 is a cross-sectional view of the pipe assembly  10  taken along the line C—C in FIG. 1, at a lengthwise position further downstream from the lengthwise position depicted in FIG.  3 . With reference to FIG. 4, the inner pipe  12  and the outer laminated pipe  14  both present a race track cross-sectional configuration. At this position, the inner pipe  12  and the outer laminated pipe  14  are in substantially spaced relation to reduce thermal dissipation to the outer pipe  14 . The outer pipe  14  is displaced radially outward from the inner pipe  12  by a separation distance measured from the outer surface of the inner pipe  12  to the inner surface of the inner layer  22 . 
     FIG. 5 is a cross-sectional view of the downstream outlet portion of the pipe assembly  10  taken along the line D—D in FIG.  1 . With reference to FIG. 5, the downstream outlet portion of the pipe assembly presents a substantially D-shaped cross-sectional configuration. Both the inner pipe  12  and the outer laminated pipe  14  present such a D-shaped configuration at the downstream outlet portion. The inner pipe  12  and the outer laminated pipe  14  are in contact according to the principles of the invention at three areas, as shown in FIG. 5, to optimally support the outer pipe  14 . The outer laminated pipe  14  presents a substantially planar side wall  28  at the downstream outlet portion  18  (FIG.  1 ). A pair of such pipe assemblies, having their planar side walls positioned adjacent to each other, can fit through the circular opening of an outlet flange. 
     At the upstream inlet portion  16  (FIG. 1) of the pipe assembly  10 , the inner pipe  12  consistently contacts the surrounding outer laminated pipe  14 , as shown in FIG.  2 . At the downstream outlet portion  18  of the pipe assembly  10 , the inner pipe  12  abuts the inner layer  22  of the outer pipe  14  at three contacting areas spaced from each other on the outer pipe  14  to optimally stabilize the pipes, as shown in FIG.  5 . The arrangement shown in FIG. 5 provides thermal insulation of the inner pipe  12  by way of an air-filled space  38  at least partially separating the inner pipe  12  and the outer pipe  14 . 
     By way of example and not limitation, the pipe assembly is subsequently described as embodied in an exhaust manifold illustrated in FIG. 6 according to a specific embodiment of the invention. The exhaust manifold shown in FIG. 6 includes a set  34  of pipe assemblies connecting the cylinders of an internal combustion engine (not shown) to exhaust pipes (not shown) located downstream from the cylinders. Each pipe assembly  10  includes an outer pipe  14  and an inner pipe  12  located within and surrounded by the outer pipe  14 . The outer pipe  14  includes an outer layer  24  and an inner layer  22 , where the inner layer  22  is attached to the outer layer  24 , preferably laminated; and the outer layer  24  has a thickness selected in relation to and based upon the thickness of the inner layer  22  to optimally reduce noise emitted from the set  34  of pipe assemblies according to the specific embodiment of the invention. The outer layer  24  of the outer pipe  14  is preferably approximately twice the thickness of the inner layer  22  of the outer pipe  14 . For example, the outer layer  24  of the outer pipe  14  has a thickness of 0.8 mm while the inner layer  22  of the outer pipe  14  has a thickness of 0.4 mm. The outer layer  24  and the inner layer  22  each present a smooth surface to facilitate lamination thereof. 
     The exhaust manifold shown in FIG. 6 includes an inlet flange  42  which is mountable on an internal combustion engine. The inlet flange  42  defines a group of inlet openings  44  which when the inlet flange  42  is mounted to the internal combustion engine correspond to the location of exhaust ports of cylinders of the internal combustion engine, and through which exhaust gases can move. Each inlet opening  44  is associated with a respective exhaust port. 
     The inlet flange  42  defines one or more bolt holes  46  through which a bolt or other fastening means can extend to fasten the inlet flange  42  to the internal combustion engine so that the inlet openings  44  of the inlet flange  42  are aligned with the exhaust ports of the internal combustion engine. 
     Four inlet openings  44  are illustrated in FIG.  6 . In the exhaust manifold shown in FIG. 6, each of the four pipe assemblies, such as pipe assembly  10 , is connected at its upstream inlet portion to one of the four inlet openings  44  in the inlet flange  42  so that exhaust gases can pass from the respective exhaust port, through the respective inlet opening into the upstream inlet portion of such pipe assembly  10 . 
     Each of the pipe assemblies is connected at its downstream outlet portion to an outlet flange  50 . The outlet flange  50  is connectable to a number of downstream pipes. The outlet flange  50  defines a plurality of outlet openings  52 . The number of outlet openings  52  in the outlet flange  50  is half the number of pipe assemblies according to the specific embodiment of the invention illustrated in FIG.  6 . The outlet openings  52  defined by the outlet flange  50  connect pairs of pipe assemblies to an associated downstream pipe, and provide a conduit through which exhaust gases can move from the pipe assemblies to the downstream pipes. The outlet flange  50  defines one or more bolt holes  54  through which a bolt or other fastening means can pass to fasten and align the outlet flange to the downstream pipes. 
     From the foregoing, it will be appreciated that noise emitted from the pipe assemblies is reduced according to the principles of the invention by laminating the outer layer and the inner layer of the outer pipe and selecting the respective thicknesses of the outer layer and the inner layer in relation to each other. 
     While several particular forms of the invention have been illustrated and described, it will also be apparent that various modifications can be made without departing from the spirit and scope of the invention.