Abstract:
An embodiment of a heat shield provides a sheet metal layer selectively facing a heat source and a plastic layer coupled to the sheet metal layer. The heat shield further includes an insulation layer at least partially interposed between the sheet metal layer and the plastic layer.

Description:
TECHNICAL FIELD  
       [0001]     The technical field relates to protective heat shields for vehicular engine parts, such as engine exhaust manifolds that transmit substantial heat and vibration during engine operation. More specifically, the technical field relates to fabrication of protective heat shields and novel application of structures that may reduce weight and costs and increase the dampening of such heat shields.  
       BACKGROUND  
       [0002]     The exhaust manifolds of internal combustion engines in today&#39;s modern vehicles can reach under-the-hood temperatures exceeding 1600 degrees Fahrenheit. Such high temperatures create significant risks of damage to electronic components sharing under-the-hood space with the manifolds. Thus, protection has been provided for such components via use of heat shields designed to at least partially cover up and insulate exhaust manifolds and other heat generating components. In some cases, the shields have been effective to reduce measured temperature levels to within a range of 300 degrees Fahrenheit.  
         [0003]     A typical multilayer heat shield positioned adjacent a component such as an exhaust manifold uses spaced layers of metal with air gaps between the layers. These typical heat shields transmit heat along the layer directly adjacent the component while the next adjacent layer is insulated from this heat by the air gap. Since the metal layers are free to vibrate, they typically respond to resonate frequencies, or frequencies that are transmitted through contact, and transmit undesired noise. Other multilayer heat shields use metal layers with insulation interposed between the layers. Unlike heat shields without insulation, the insulation dampens the vibrations of the metal layers at locations of contact. Typically, a normal, inward force is provided between the metal layers to ensure increased contact between the insulation and metal layers in order to dampen the vibrations in the metal layers.  
         [0004]     The outer metal layer is typically formed of aluminized sheet steel. In order to increase the effectiveness of the shields and reduce the space required for the shields, the metal layers are typically contoured to closely resemble the shape of the outer surface of the exhaust manifold. To provide the desired contour in sheet steel, a generally planar piece of steel is stamped or formed in a progressive die. The resulting outer metal layer of a heat shield typically includes a number of wrinkles. These wrinkles reduce the aesthetic appearance of the heat shields, thin any anti-corrosion coating that may be applied, provide thinned brittle stress regions for future areas of cracking and other failures, and decrease the natural frequency of the heat shield in the region of the wrinkle which may excite frequencies in other regions of higher natural frequency in the heat shield and increase noise transmission. The outer metal layer of a typical heat shield also increases weight and cost.  
         [0005]      FIG. 1  illustrates an engine  20 . Engine  20  includes a cylinder head  24 , an exhaust manifold  26 , and a prior art heat shield  30 . The heat shield  30  is adapted to closely surround at least portions of the exhaust manifold  26 . The exhaust manifold  26  is bolted via bolts (not shown) to a plurality of engine exhaust ports  40  on the flank or side  42 , of the cylinder head  24 .  
         [0006]     The exhaust manifold  26  includes cooperating ports (not numbered) in fluid communication with exhaust ports  40 . The exhaust manifold  26  also includes mounting bosses  50  for attachment of the heat shield  30  to the exhaust manifold  26  via bolts  52 . The engine exhaust ports  40  operate to collectively receive exhaust gases from individual combustion chambers (not shown) of the engine  20 , and to funnel those exhaust gases into a common exhaust pipe portion (not shown) of the exhaust manifold  26 .  
         [0007]     The prior art heat shield  30  includes a contoured outer surface  62  that is formed from a layer of sheet steel to closely contour the outer surface of the exhaust manifold. Outer surface  62  includes wrinkles  64  resulting from the forming operation that produces the prior art heat shield  30 .  
         [0008]     While prior art heat shields perform adequately for their intended purposes, heat shields are an area of constant innovation to provide lighter, quieter, less expensive, and more aesthetically pleasing components.  
       SUMMARY  
       [0009]     An embodiment of a heat shield provides a sheet metal layer selectively facing a heat source and a plastic layer coupled to the sheet metal layer. The heat shield further includes an insulation layer at least partially interposed between the sheet metal layer and the plastic layer.  
         [0010]     In a further embodiment, a heat shield includes an outer plastic layer having a first outer surface, a second outer surface, and an outer edge, and an inner metal layer defined, at least in part, by a first inner surface, a second inner surface, and a peripheral edge. The inner metal layer is selectively positioned directly proximal to a shielded component. At least portions of the first outer surface and the second inner surface define a gap therebetween.  
         [0011]     In another embodiment, a method of manufacturing a heat shield includes the steps of forming an outer plastic layer, forming an inner metallic layer, and positioning the outer layer adjacent the inner layer. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a partial side elevation view of an engine having a prior art heat shield.  
         [0013]      FIG. 2  is a partial side elevation view of a portion of an engine illustrating an embodiment of a heat shield.  
         [0014]      FIG. 3  is a partial sectional view of the heat shield of  FIG. 2  taken along fragmented line  3 - 3  of  FIG. 2 .  
         [0015]      FIG. 4  is an enlarged partial fragmentary view of the heat shield of  FIG. 2  taken along line  4 - 4  of  FIG. 2 .  
     
    
     DETAILED DESCRIPTION  
       [0016]      FIGS. 2 and 3  illustrate a portion of an engine  120 . Engine  120  includes a cylinder head  124 , an exhaust manifold  126 , and a heat shield  130 . The heat shield  130  is adapted to surround at least portions of the exhaust manifold  126 . The exhaust manifold  126  is operatively secured via fasteners (not shown) to a plurality of engine exhaust ports  140  on the flank or side  142 , of the cylinder head  124 . Such fasteners may include bolts or other suitable fasteners known in the art.  
         [0017]     The exhaust manifold  126  includes cooperating ports  144  ( FIG. 3 ) in fluid communication with exhaust ports  140 . The exhaust manifold  126  may also include mounting bosses  150  for attachment of the heat shield  130  to the exhaust manifold  126  via fasteners  152 . The engine exhaust ports  140  operate to collectively receive exhaust gases from individual combustion chambers (not shown) of the engine  120 , and to funnel those exhaust gases into a common exhaust pipe portion  158  ( FIG. 3 ) of the exhaust manifold  126 .  
         [0018]     As best seen in  FIGS. 3 and 4 , the heat shield  130  includes a contoured body  160 . The contoured body  160  dampens the structure of heat shield  130 , thereby permitting heat shield  130  to attenuate vibrations, as described in greater detail below.  
         [0019]     In  FIG. 4 , a partial cross-section of heat shield  130  is illustrated. Heat shield  130  is made up of a plurality of layers, such as an inner metal layer  170 , and an outer layer  172 , with an insulation layer  174  interposed therebetween. Inner metal layer  170  includes a first inner surface  180  that faces insulation layer  174 , a second inner surface  182 , and a peripheral edge  188 . Outer layer  172  includes a first outer surface  190  that faces insulation layer  174 , a second outer surface  192 , and an outer edge  198 . Insulation layer  174  includes an inner surface  200  that faces inner metal layer  170  and an outer surface  202  that faces outer layer  172 .  
         [0020]     At least a portion of peripheral edge  188  of inner metal layer  172  is folded over outer edge  198  of outer layer  170 . In one embodiment, a sufficient amount of peripheral edge  188  is folded over, or overlays, outer edge  198  to retain insulation  174  therein and to couple layers  170 ,  172 .  
         [0021]     While heat shield  130  is illustrated in  FIG. 4  as having an insulation layer  174  interposed in a gap between layers  170 ,  172 , layers  170 ,  172  may be provided with no insulation layer  174  or a partial insulation layer  174 . Additionally, insulation layer  174  may be at least partially absent and the gap remain between portions of layers  170 ,  172 . Also contemplated is an embodiment of heat shield  130  where first inner surface  180  contacts portions of first outer surface  190 .  
         [0022]     In one embodiment, outer layer  172  is a layer of plastic material that retains insulation layer  174  in position and protects insulation layer  174  from environmental degradation. Outer layer  172  may be injection molded in a mold that produces an aesthetically pleasing second outer surface  192 , or may be shaped from a piece of plastic material to form a desired shape.  
         [0023]     As best seen in comparing  FIGS. 1 and 2 , the formation of outer layer  172  as a plastic component allows for an aesthetically curved second outer surface  192  such that surface wrinkles  64  of the prior art heat shield  30  are less pronounced or nonexistant. Also, an embodiment of outer layer  172  formed of plastic will reduce the vibrations transmitted from engine  120  as plastic will generally dampen vibrations when compared to a metal layer.  
         [0024]     During operation of heat shield  130 , inner metal layer  170  is generally at a greater temperature than outer layer  172 . Therefore, inner metal layer  170  will expand more than outer layer  172 . The differential expansion of layers will create a small normal force inwardly interacting between the inner metal layer  170  and the outer layer  172 . The thicknesses and coefficients of thermal expansion of layers  170 ,  172  can effect the generally normal force between these layers.  
         [0025]     Although described with three layers, the heat shield  130  could be effectively manufactured with additional layers, or with insulation layer  174  applied in selective regions of heat shield  130 . The inner metal layer  170  would provide the requisite stiffness and support in such cases, but may need to be relatively thicker in some applications. While heat shield  130  is depicted as a heat shield for an exhaust manifold, heat shield  130  may be formed in various desired shapes and other components may be shielded.  
         [0026]     The material choices for the thermally insulating and vibration and noise dampening insulation layer  174  are fairly broad. Such choices may include non-metallic fibers such as aramid fibers, or ceramic fiber paper. Depending on anticipated temperature ranges, even non-fiber compositions may be employed, such as densified vermiculite powders, for example.  
         [0027]     The inner metal layer  170  is the portion of the heat shield  130  in closest proximity to the exhaust manifold  126 . To the extent that the temperatures of the manifold can reach 1600 degrees Fahrenheit, the material of the inner metal layer  170  should be able to withstand significant heat. In some applications the inner metal layer  170  may be relatively shiny, formed of high-temperature alloys, and adapted to reflect heat back to the shielded component. In others, the inner metal layer  170  can be of less expensive materials including aluminum-clad steel. Inner metal layer  170  may also have wrinkles similar to wrinkles  64 . Those skilled in the art will appreciate that choice of materials may be critical for avoiding degradation associated with elevated temperatures and for handling considerable vibrations in particular applications.  
         [0028]     In one embodiment, inner metal layer  170  is aluminumized steel with a thickness between the first inner surface  180  and the second inner surface  182  of about 0.010 to about 0.030 inch. Even more preferably, inner metal layer  170  is aluminumized steel with a thickness between the first inner surface  180  and the second inner surface  182  of about 0.016 to about 0.020 inch. In the embodiment illustrated, inner metal layer  170  provides a significant amount of the structural support of the heat shield  130 , although outer layer  172  may be formed of a material that provides structural support to the body  160  of heat shield  130 .  
         [0029]     One exemplary method of manufacturing of the heat shield  130  can be described as follows. The inner metal layer  170  and the outer layer  172  are preferably formed in separate operations. The inner metal layer  170  is positioned within a progressive die (not shown). The inner metal layer  170  is then stamped and formed in the progressive die to the shape depicted in  FIGS. 2-4 . The inner metal layer  170  may be trimmed either before, after, or during stamping.  
         [0030]     In the embodiment illustrated, the outer layer  172  is formed separately then layered with the insulation layer  174  and inner metal layer  170 . An injection molding process or other plastic forming process may be used to form outer layer  172  with a desired thickness. The desired thickness of the outer layer may be determined by a desired structural stiffness, desired resonate frequency ranges, and/or resistance to buckling at operating temperatures.  
         [0031]     Also in the embodiment illustrated, the inner metal layer  170  will be relatively and slightly oversized compared to the outer layer  172 , so that the peripheral edge  188  of the inner metal layer  170  may be folded over, or crimped onto, the outer edge  198  to at least partially enclose outer edge  198  of the outer layer  172 . This crimping effectively retains the insulation layer  174  between the layers  170 ,  172 . While layers  170 ,  172  are described as being coupled by crimping, other coupling devices and methods may be utilized to produce a heat shield  130 .  
         [0032]     It is to be understood that the above description is intended to be illustrative and not limiting. Many embodiments will be apparent to those of skill in the art upon reading the above description. Therefore, the scope of the invention should be determined, not with reference to the above description, but instead with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.