Abstract:
A multi-layer heat shield with complementary contours or dimples formed in adjacent layers. The dimples provide contact between layers that dampen vibrations. The dimples may be formed concurrently in all layers with a stamping die. The dimples increase the heat shield&#39;s damping.

Description:
FIELD OF INVENTION  
       [0001]     The present invention 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 invention relates to fabrication of protective heat shields and novel application of structures that increase the damping 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 metal layers with air gaps between the layers. These 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. However, since the metal layers are free to vibrate, they typically resonate and transmit undesired noise.  
         [0004]     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. However, these heat shields may vibrate in areas without contact between the layers, thereby transmitting noise.  
         [0005]     The outer metal layer is typically formed of aluminized sheet steel. To increase the effectiveness of the shield and reduce the space required for the shield, the metal layers may be contoured to closely resemble the shape of the outer surface of the exhaust manifold. To provide the desired contour in sheet steel, 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.  
         [0006]     An example of the above described prior art heat shield for an exhaust manifold is illustrated in  FIG. 1 . The prior art heat shield  10  includes a contoured outer surface  12  that is formed from a layer of sheet steel to closely contour the outer surface of an exhaust manifold as can be seen. Outer surface  12  includes wrinkles  14  resulting from the forming operation that produces the prior art heat shield  10 . These wrinkles reduce the aesthetic appeal of the engine compartment of an automobile.  
       SUMMARY  
       [0007]     The present invention provides an improved multilayer insulated heat shield for engine components, such as exhaust manifolds of internal combustion engines. In accordance with one aspect of the invention, metal layers of the heat shield are dimpled, or otherwise contoured to provide increased surface area for heat transfer, reduce wrinkling, improve aesthetics, strengthen the heat shield from bending, and/or to provide a heat shield with a narrower range of natural frequencies in differing regions.  
         [0008]     In one embodiment, a heat shield includes at least three layers. An outer layer has outer dimples formed therein. An inner layer has inner dimples formed therein. At least a portion of the inner dimples and the outer dimples are nested. An insulating layer is positioned between the inner layer and the outer layer.  
         [0009]     In another embodiment, a heat shield for an under-the-hood vehicular engine component includes an outer metal layer, an inner metal layer selectively positioned directly proximal to a shielded component, and an insulation layer partially between the metal layers. The outer metal layer and the inner metal layer are dimpled. The insulation layer is interposed at least partially between the metal layers and the dimples of the metal layers interact to dampen vibrations of the heat shield.  
         [0010]     A method of manufacturing a heat shield in accordance with the present invention is also disclosed. The inventive method includes forming outer dimples in an outer layer, and forming inner dimples in an inner layer. At least a portion of the outer dimples and at least a portion of the inner dimples are nested when the outer layer is positioned adjacent the inner layer. The method further includes positioning the outer layer adjacent the inner layer. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a side elevation view of a prior art heat shield.  
         [0012]      FIG. 2  is a side elevation view of a portion of an engine, illustrating an embodiment of a heat shield in accordance with the present invention.  
         [0013]      FIG. 3  is a sectional view of the heat shield of  FIG. 2 , taken along fragmented line  3 - 3 .  
         [0014]      FIG. 4  is a side elevation view of an embodiment of a heat shield in accordance with the present invention.  
         [0015]      FIG. 5  is an enlarged sectional view of a portion of the heat shield of  FIG. 4 , with background portions removed for clarity.  
         [0016]      FIG. 6  is a fragmentary view a further embodiment of a heat shield surface.  
     
    
     DETAILED DESCRIPTION  
       [0017]      FIGS. 2 and 3  illustrate a portion of an engine  20 . Engine  20  includes a cylinder head  24 , an exhaust manifold  26 , and a heat shield  30 . The heat shield  30  is adapted to encase or 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 .  
         [0018]     The exhaust manifold  26  includes cooperating ports  44  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  58  of the exhaust manifold  26 .  
         [0019]     As best seen in  FIGS. 3, 4  and  5 , the heat shield  30  includes a contoured body  60 . The contoured body  60  dampens the structure of heat shield  30 , thereby permitting heat shield  30  to attenuate vibrations, as described in greater detail below.  
         [0020]      FIG. 5  illustrates heat shield  30  to include an inner metal layer  70 , and an outer metal layer  72 , with an insulation layer  74  interposed therebetween. Inner metal layer  70  includes a first inner surface  80  and a second inner surface  82  that faces insulation layer  74 , with inner dimples  84  formed therein. Outer metal layer  72  includes a first outer surface  90  that faces insulation layer  74  and a second outer surface  92 , with outer dimples  94  formed therein. Insulation layer  74  includes an inner surface  100  that faces inner metal layer  70  and an outer surface  102  that faces outer metal layer  72 , with insulation dimples  104  formed therein.  
         [0021]     As best seen in  FIG. 5 , the inner metal layer  70 , the outer metal layer  72 , and the insulation layer  74  are positioned such that the inner dimples  84 , the outer dimples  94 , and the insulation dimples  104  are at least partially nested. Nested refers to the condition where a dimples resides within another dimple. Specifically, one inner dimple  84  and one outer dimple  94  are nested when a portion of the inner dimple  84  intersects a plane (illustrated as plane P-P in  FIG. 5 ) generally defined by first outer surface  90 . Testing of a representative heat shield  30  having nested dimples demonstrated a 27% increase in damping factor over an undimpled heat shield. Alternatively, insulation layer  74  may be thicker such that at least a portion of inner dimples  84  and outer dimples  94  may be aligned and not nested to provide some degree of vibration dampening.  
         [0022]     During operation of heat shield  30 , inner metal layer  70  is generally at a greater temperature than outer metal layer  72 . Therefore, inner metal layer  70  will expand more than outer metal layer  72 . The differential expansion of layers will create a small normal force inwardly interacting between the inner metal layer  70  and the outer metal layer  72 . In addition to the normal force that may exist for both the prior art heat shield  10  and the heat shield  30 , inner dimples  84  and outer dimples  94  interact with the insulation dimples  104  of the insulation layer  74  to dampen vibrations within the inner metal layer  70  and the outer metal layer  72 . Dimples  84 ,  94  increase the area of contact between layers  70 ,  72 , and  74 , thereby increasing the dampening of heat shield  30 .  
         [0023]     Preferably, outer dimples  94  are randomly scattered and not aligned within outer metal layer  72  in such a manner that would create an undesirable bending plane within the outer metal layer  72  and heat shield  30 . While the curvature of an exhaust manifold heat shield in accordance with the teachings herein may be less susceptible to bending than a larger, less curved heat shield, an exhaust manifold heat shield would benefit from a scattering of dimples  84 ,  94 . Alternatively, a repetitive pattern  114  of dimples  84 ′,  94 ′,  104 ′, as illustrated in  FIG. 6 , may be formed in layers  70 ′,  72 ′,  74 ′ to attenuate vibrations while discouraging an undesirable bending plane.  
         [0024]     As best seen in  FIGS. 1 and 4 , the formation of outer dimples  94  act to stretch the skin of outer metal layer  72  such that surface wrinkles  14  of the prior art heat shield  10  are less pronounced. In this manner, outer dimples  94  improve the aesthetic appeal of heat shield  30  while decreasing the undesirable effects of wrinkles  14 , such as thinning any anti-corrosion coating that may be applied and creating thinned brittle stress regions for future areas of cracking and other failures.  
         [0025]     The outer metal layer  72  may be preferably formed of cold rolled steel, aluminized steel, aluminum, and even stainless steel for more exotic vehicles where cost is less of a factor. If cold rolled steel is utilized, the exterior of the shield may be coated with a corrosion-resistant material to enhance longevity of the shield.  
         [0026]     The inner metal layer  70  is the portion of the heat shield  30  in closest contact with the exhaust manifold  26 . To the extent that the temperatures of the manifold can reach 1600 degrees Fahrenheit, the material of the inner metal layer  70  should be able to withstand significant heat. In some applications the inner metal layer  70  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  70  can be of cheaper materials including aluminum-clad steel. 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.  
         [0027]     Although described with three layers, the heat shield  30  could be effectively manufactured with additional layers, or with insulation layer  74  applied in selective regions of heat shield  30 . The inner metal layer  70  would provide the requisite stiffness and support in such cases, but may need to be relatively thicker in some applications. Additionally, while outer dimples  94  and inner dimples  84  are illustrated as extending away from exhaust manifold  26 , the all or a portion of the dimples  84 ,  94  may extend toward exhaust manifold  26 .  
         [0028]     The material choices for the thermally insulating and vibration and noise dampening insulation layer  74  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.  
         [0029]     One method of manufacturing of the heat shield  30  can be described as follows. The inner metal layer  70  and the outer metal layer  72  with the insulation layer  74  interposed between are positioned within a progressive die (not shown). The layers  70 ,  72 ,  74  are stamped and formed in the progressive die to the shapes depicted, including the dimples  84 ,  94 ,  104 . The layers  70 ,  72 ,  74  may be trimmed either before, after, or during stamping. The progressive die includes male and female forming tools that are pressed together with layers  70 ,  72 ,  74  positioned therebetween. The male and female forming tools have complementary surfaces cut therein to form dimples  84 ,  94 ,  104 .  
         [0030]     As the male and female forming tools are pressed together, layers  70 ,  72 ,  74  are formed into the general shape depicted in  FIGS. 2 and 3  without significant dimple formation. In the last few millimeters of die travel, the dimples  84 ,  94 ,  104  are formed within the layers  70 ,  72 ,  74 . The outer edges of layers  70 ,  72  are then attached, such as by crimping, and may be crimped before removal from the progressive die.  
         [0031]     As best seen in  FIGS. 3 and 5 , when heat shield  30  is formed with a contoured body  60 , and outer edges of layers  70 ,  72  are attached, such as by crimping, the dimples  84 ,  94 ,  104  are held in contact by the normal force that exists between the layers due to the curvature of heat shield  30 . This normal force in a contoured body  60  increases contact between dimples  84 ,  94 ,  104 , although a planar heat shield would benefit from the interaction between dimples of adjacent layers.  
         [0032]     Alternatively, the inner metal layer  70  and the outer metal layer  72  may be formed separately in the general shape depicted in  FIGS. 2 and 3  without dimples  84 ,  94 , then layered with the insulation layer  74 , and then stamped in a die to form the dimples  84 ,  94 ,  104 .  
         [0033]     Preferably, the outer metal layer  72  will be relatively and slightly oversized compared to inner metal layer  70 , so that edges (not shown) of the outer metal layer  72  may be folded over respective mated edges of the inner metal layer  70 , effectively encapsulating the insulation layer  74  between the layers  70 ,  72 . Dimples  84 ,  94  may be generally hemispherical or have a generally conical portion.  
         [0034]     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.