Abstract:
An exhaust manifold gasket having a gasket body including at least two metal plates defining a first surface and a second surface is described herein. The body has a plurality of service openings defining at least one exhaust hole and a plurality of bolt holes. The second surface includes a foldover around a perimeter of the body. A thermally resistant layer may be located between the first surface and the second surface and extends beyond a sealing region of the gasket. A load limiting layer that works to prevent excess compression at the bolt holes is disposed proximate a metal plate.

Description:
CROSS-REFERENCE To RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application Ser. No. 60/586,612 filed Jul. 9, 2004, which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD  
       [0002]     The embodiments of the invention described herein are generally directed to insulating exhaust manifold gaskets.  
       BACKGROUND  
       [0003]     An engine and a gasket installed therein for an automobile include exhaust ports, water holes, oil holes and bolt holes. Since high pressure and temperature are developed within the exhaust ports when the engine is actuated, bolts for securing the engine parts together with the gasket are generally arranged around the exhaust ports. Tightening of the bolts creates a pressure around the exhaust ports, thereby forming a seal therearound.  
         [0004]     Traditional gaskets have used embossments, or metal sealing beads to seal around exhaust ports. These known gasket designs permit thermal conduction from the manifold to the cylinder head. Accordingly, some type of insulating material is required to prevent thermal damage from occurring to the cylinder head or other nearby engine components. However, insulating material as a seal is typically unsatisfactory as it tends to have a low density and therefore a high material compression, particularly around the bolts where the entire load was being applied. Because of the high degree of material compression, manifold flanges would deform so as to bend around the more rigid sealing area of the gasket, thereby causing an undesirable leak path. Accordingly, there is a need for an insulating heat shield gasket that prevents undesirable leakage.  
         [0005]     Standard foldover style gaskets incorporate load limiting/load balancing features both around the port being sealed and gasket perimeter by perimeter foldovers. Integrating a heat shield with geometry extending beyond the required gasket prevents the use of a perimeter foldover to control load balancing (perimeter compression) and load limiting at the bolts. Therefore, it would be desirable to integrate a separate the load limiting layer into the gasket. The perimeter foldover is therefore not used for load balance purposes, but to contain the filler material.  
       SUMMARY  
       [0006]     The embodiments described herein provide an exhaust manifold gasket having a gasket body including at least two metal plates defining a first layer and a second layer. The body has a plurality of service openings defining at least one exhaust hole and a plurality of bolt holes. Either the first or the second layer includes a metal foldover around a perimeter of the body. A thermally resistant layer may be located between the first layer and the second layer including a plurality of service openings corresponding to the body and can extend beyond the required sealing area of the gasket to provide heat shielding to other engine components. In one embodiment, a load limiting layer is located on the upper surface of the first layer of the gasket. In another embodiment, the load limiting layer is located between the first layer and the thermally resistant layer, where the load limiting layer works to prevent excess compression at the bolt holes and provide proper exhaust port sealing of the outer exhaust manifold surface perimeter. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The features and inventive aspects of the present invention will become more apparent upon reading the following detailed description, claims, and drawings, of which the following is a brief description:  
         [0008]      FIG. 1  is a plan view of a first embodiment of an insulating exhaust manifold gasket showing a load limiting layer on a surface of the gasket;  
         [0009]      FIG. 2  is a cross-sectional view of the insulating exhaust manifold gasket taken along lines  2 - 2  of  FIG. 1 ;  
         [0010]      FIG. 3  is a cross-sectional view of the insulating exhaust manifold gasket taken along lines  3 - 3  of  FIG. 1 ;  
         [0011]      FIG. 4  is a cross-sectional view of the insulating exhaust manifold gasket taken along lines  4 - 4  of  FIG. 1 ;  
         [0012]      FIG. 5  is a cross-sectional view of the insulating exhaust manifold gasket taken along lines  5 - 5  of  FIG. 6 ;  
         [0013]      FIG. 6  is a plan view of a second embodiment of an insulating exhaust manifold gasket showing the load limiting layer between the upper and lower surfaces of the gasket;  
         [0014]      FIG. 7  is a cross-sectional view of the insulating exhaust manifold gasket taken along lines  7 - 7  of  FIG. 6 ;  
         [0015]      FIG. 8  is a cross-sectional view of the insulating exhaust manifold gasket taken along lines  8 - 8  of  FIG. 6 ; and  
         [0016]      FIG. 9  is a top plan view of an individual load limiter according to an embodiment of an insulating exhaust manifold gasket. 
     
    
     DETAILED DESCRIPTION  
       [0017]     Referring now to the drawings, illustrative embodiments are shown in detail. Although the drawings represent the embodiments, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain an innovative aspect of an embodiment. Further, the embodiments described herein are not intended to be exhaustive or otherwise limit or restrict the invention to the precise form and configuration shown in the drawings and disclosed in the following detailed description.  
         [0018]     Referring now to  FIGS. 1-5 , and  9 , a gasket  10  having first metal layer  12  and second metal layer  14  is disclosed. The metal layers  12 ,  14  are constructed of any steel or alloy. In one embodiment, the gasket  10  is formed from a stainless steel or a nickel alloy. The gasket  10  is held between mating joint surfaces of an exhaust manifold  13  as shown in  FIG. 9  and a cylinder head (not shown), to seal the opposing surfaces to each other. The exhaust manifold, cylinder head, and gasket  10  are fixed to each other with bolts to maintain the air tightness thereof and prevent the leakage of an exhaust gas.  
         [0019]     In accordance with another embodiment of the invention, rather than provide individual gaskets at each port, the gasket  10  is a one piece gasket and the large gasket body  15  extends between the ports. The body  15  defines a plurality of apertures or openings, including conventional exhaust port openings  16  and bolt holes  18 . The gasket  10  may also include other holes (not shown) Various sealing mechanisms such as protective coatings, beads, and the like may be provided as well.  
         [0020]     As shown in  FIG. 2 , the body  15  may include a thermally resistant layer  20  disposed between the first and second metal layers  12 ,  14  having a plurality of openings corresponding to the plurality of openings in the first and second metal layers  12 ,  14 .  
         [0021]     The materials for the thermally resistant layer  20  incorporated in the metal gasket  10  will now be described. The materials constituting the thermally resistant layer  20  include but are not limited to high temperature insulation, inorganic materials, Dana Xtreme Plus®, and, for example, a mica material, which has the following characteristics. A mica material is a natural incombustible material, and has a resistance to heat of not lower than 1000 degrees Celsius, so that it can sufficiently withstand the temperature of an exhaust gas in the exhaust port opening  16  of, for example, 800 degrees-900 degrees Celsius. Moreover, a mica material has a high corrosion resistance, a high chemical resistance, and excellent heat insulating characteristics. Any material for the thermally resistant layer may incorporate a perforated or solid steel core for rigidity. Any material for the thermally resistant layer  20  may be characterized by a low density. Insulating composite materials are used in an incompletely densified form, causing compression under load. Layer  20  may exhibit these characteristics for proper sealing.  
         [0022]     As shown in  FIG. 3 , in accordance with an embodiment, the first metal layer  12  is longer than the second metal layer  14  at a perimeter  30  of the metal gasket  10  such that a foldover  32  of the first metal layer  12  may be folded over the thermally resistant layer  20  and onto the second metal layer  14 . The foldover  32  around the exhaust port opening  16  of the metal gasket  10  works to concentrate the load onto the sealing area. In another embodiment, the second metal layer  14  may be longer than the first metal layer  12  around the perimeter  30  of the metal gasket  10  such that the foldover  32  of the second metal layer  14  may be folded over the thermally resistant layer  20  and onto an upper surface  36  of the first metal layer  12 . In yet another embodiment, the first metal layer  12  may be longer than the second metal layer  14  at predetermined edges; while the second metal layer  14  may be longer than the first metal layer  12  at other predetermined edges (not shown).  
         [0023]     A load limiting layer  34  is disposed proximate the upper surface  36  of the first metal layer  12 . In one embodiment as best shown in  FIGS. 1 and 5 , the load limiting layer  34  is assembled to the first metal layer  12  of the metal gasket  10  at the upper first surface  36  and may be attached using rivets, welding, foldovers or any other suitable attachment method. In another embodiment as shown in  FIG. 6 , the load limiting layer  34  (shown in dotted lines) is disposed between the first metal layer  12  and the thermally resistant layer  20 . The load limiting layer  34  is proximate the bolt holes  18  of the metal gasket  10  and around a flange perimeter  38  as shown in  FIG. 9 . The dotted line in  FIG. 9  represents the face surface of the mating exhaust manifold flange. The load limiting perimeter  42  represents how the load limiting layer  34  may support both the bolt hole  18  areas and exhaust manifold flange perimeter  38 . Preferably, the load limiting layer  34  is one large piece for easier assembly in production rather than individual load limiters at each exhaust manifold flange  13 . The load limiting layer  34  is used to act as a load limiter and prevent excess material compression at the bolt holes  18  as well as a load balancer to properly distribute bolt load around the exhaust port (not shown) and the flange perimeter  38 . However, individual load limiters may be utilized as the load limiting layer  34  for purposes of this disclosure. The load limiting layer  34  provides a stiffer area around the bolt holes  18  and further reduces relaxation of the thermally resistant layer  20 . Moreover, the load limiting layer  34  provides less material deflection that also aids in the elimination of relaxation of the thermally resistant layer  20 .  
         [0024]     The load limiting layer  34 , metal layers  12 ,  14 , and insulating layer  20  may include various thicknesses to best balance the bolt load between the exhaust port and manifold flange perimeter  38 .  
         [0025]     The preceding description has been presented only to illustrate and describe exemplary embodiments of the methods and systems of the present invention. It is not intended to be exhaustive or to limit the invention to any precise form disclosed. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. The invention may be practiced otherwise than is specifically explained and illustrated without departing from its spirit or scope. The scope of the invention is limited solely the following claims.