Patent Publication Number: US-2006012131-A1

Title: Fluid aperture with stopper bead

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of U.S. Provisional Application Ser. No. 60/588,451 filed Jul. 16, 2004 which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND  
      The present invention relates generally to improvements in multi-layered steel (MLS) cylinder head gaskets for automotive internal combustion engines. More specifically, the present invention relates to an MLS gasket having a protective sealing bead around a fluid aperture in the gasket.  
      In recent years, MLS cylinder head gaskets have become a preferred design, wherein all (typically at least two) gasket layers have been formed from steel. In a typical MLS gasket design, the gasket is provided with a plurality of openings. More specifically, known gaskets include cylinder bore openings, water holes, bolt holes and oil holes. The bolt holes, which are generally located around the periphery of the gasket, cooperate with bolts to secure the gasket between the cylinder head and engine block. The cylinder bore openings, water holes and oil holes are sealed by surface pressures formed by the clamping action of the bolts.  
      Generally, when the bolts are tightened, the surface pressures varies throughout the sealing joint, especially the areas surrounding the other fluid openings, such as oil holes, do not have equal surface pressures formed therearound.  
      With respect to oil holes, for example, to compensate for unequal surface pressures, one solution has been to provide a half bead around the periphery of the oil hole. However, during extreme operating conditions, the half bead becomes crushed between the cylinder head and engine block, thereby destroying recovery potential, and hence the sealing effectiveness of the half bead. As a result, leaks are still experienced. Therefore, there is a need to provide a sealing mechanism that prevents the half bead from being damaged or destroyed, while eliminating potential leaks.  
     SUMMARY  
      An embodiment of the present invention is directed to a multi-layered cylinder head gasket having at least two metal layers. Each of the metal layers is formed with a plurality of openings. The layers are positioned in a stacked relationship to form the gasket. When stacked, the plurality of openings formed in the metal layers become aligned. A half sealing bead that extends outwardly from upper and lower surfaces of the gasket surrounds a periphery of at least one of the aligned openings. A support bead is positioned adjacent to the half sealing bead and away from the periphery of the aligned openings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings illustrate various embodiments of the present apparatus and are a part of the specification. The illustrated embodiments are merely examples of the present apparatus and do not limit the scope of the disclosure.  
       FIG. 1  is a plan view of one embodiment of an MLS cylinder head gasket in accordance with the present invention;  
       FIG. 2  is an enlarged plan view of a fragmentary portion marked as area  2  of the gasket of  FIG. 1 ;  
       FIG. 3  is a cross sectional view of an oil opening formed in the MLS gasket taken along lines  3 - 3  of  FIG. 2 . 
    
    
     DETAILED DESCRIPTION  
      As seen in  FIG. 1 , the gasket of the present invention is generally referred to at  10 . The gasket  10  includes a plurality of apertures such as bolt holes  12 , combustion openings  14  that mate with corresponding apertures of a cylinder head (not shown) and cylinder block (not shown), and oil holes  16 . When fully assembled, the gasket  10  is positioned between the cylinder head and cylinder block to fill gaps and seal around various holes and openings  12 ,  14 , and  16 . The seal generated by gasket  10  serves to prevent leaks and contamination.  
      Gaps between the cylinder head and cylinder block are created when fasteners (not shown) such as a bolt are positioned through bolt holes  12 , and are tightened to mate the cylinder head and cylinder block. These gaps result in unequal sealing stresses around the bolt holes  12 , the combustion openings  14 , the oil holes  16 , and other fluid apertures (not shown). Furthermore, the gasket  10  is subject to high loads in compression. The high compression loading generates higher stresses that may result in failure of the gasket  10 , such as cracking. An exemplary embodiment of the present invention will herein be described with attention to the sealing stresses generated about the oil holes  16 . However, gasket  10  of the present invention may incorporate the described features about any aperture. Furthermore, various embodiments of the multi-layered gasket  10  are shown throughout the Figures and similar reference numerals are used throughout  FIGS. 1-3 .  
      As shown more clearly in  FIGS. 2 and 3 , gasket  10  is a multi-layered gasket  10  having at least a first metal layer  18  and a second metal layer  20 . Gasket  10  preferably further includes a third metal layer  22 . Third layer  22  is a relatively thick metal layer, and is generally called a spacer layer. Third layer  22  is sandwiched between first and second metal layers  18 ,  20 . First and second metal layers  18 ,  20  are relatively thin in comparison with third layer  22  and are preferably constructed of 301 stainless steel, a relatively robust metal with a high spring rate for meeting requisite performance requirements over a useful gasket life. Third layer  22  is preferably formed of a less robust metal, such as 409 stainless steel, or in some cases even zinc-plated or plain low carbon steels. Each of the metal layers  18 ,  20 ,  22  include corresponding combustion bore openings  14 , bolt holes  12  and oil holes  16  formed therein such that all of the holes and openings of each gasket layer  18 ,  20 ,  22  align when assembled into gasket  10 .  
      As shown best in  FIG. 3 , an oil hole  16  is positioned adjacent bolt hole  12 . To address the uneven sealing pressures created by the bolt hole  12 , oil hole  16  is provided with a half bead  24  that surrounds the periphery  26  of oil hole  16 . Half bead  24  is formed by first metal layer  18  in cooperation with second metal layer  20 . First metal layer  18  includes an upwardly extending leg portion  28  that terminates in a generally laterally extending foot portion  30 , such that half bead  24  is raised upwardly from a top surface  32  of first metal layer  18 . Foot portion  30  extends to the periphery  26  of oil hole  16 .  
      Second metal layer  20  includes a leg portion  34  that extends downwardly from a bottom surface  36  of second metal layer  20 . Leg portion  34  terminates in generally laterally extending foot portion  38 . The leg portions  28 ,  34  and foot portions  30 ,  38  of first and second plates  18 ,  20  cooperate to form half bead  24 . The length of leg portions  28 ,  34  are selected to obtain a predetermined bead height H to provide the appropriate level of sealing for oil hole  16 .  
      In accordance with another aspect of the invention, gasket  10  may further be provided with a support bead  40  that is positioned outbound of oil hole  16  adjacent to half bead  24 . In one preferred embodiment, support bead  40  is spaced from half bead  24  by a predetermined distance D. Similar to half bead  24 , support bead  40  is formed by first metal layer  18  in cooperation with second metal layer  20 . More specifically, first metal layer  18  includes a first leg portion  42  that extends upwardly from top surface  32  of first metal layer  18 . First leg portion  42  terminates in a generally planar apex portion  44 . Connected to generally planar apex portion  44  opposite first leg portion  42  is a second leg portion  46  that extends downwardly from generally planar apex portion  44  in a similar manner as first leg portion  42 .  
      Second metal layer  20  includes a first leg portion  48  that extends downwardly from bottom surface  36  of second metal layer  20  and terminates in a generally planar base portion  50 . Connected to generally planar base portion  50  opposite first leg portion  48  is an upwardly extending second leg portion  52 . The leg portions  42 ,  46 ,  48 , and  52  and apex and base portions  44  and  50 , of first and second plates  18 ,  20  cooperate to form support bead  40 .  
      In accordance with one aspect of one embodiment, the length of leg portions  42 ,  46 ,  48 , and  52  are selected to obtain a predetermined bead height h to provide the appropriate level of sealing for oil hole  16 , without compromising the sealing characteristics of half bead  24 . More specifically, support bead  40  is formed so as to have a height h that is somewhat less than the bead height H of half bead  24 . Thus, support bead  40 , which extends outwardly from the outer surfaces  32 ,  36  of first and second metal plates  18 ,  20  in opposite directions is stiff enough to limit crushing of half bead  24  between the engine block and the cylinder head, thereby preserving the recovery characteristics of half bead  24  during thermal expansions and contractions. In one embodiment, support bead  40  extends at least partially around half bead  24 . In another embodiment, support bead  40  extends completely around half bead  24 .  
      Because cylinder heads and engine blocks for different engines have different thermal effects, the appropriate height and load deflection behavior of the support bead  40  are critical. First, the sealing pressure of the gasket  10  and in particular the area around the oil holes  16  needs be determined. Finite element analysis is one desirable method to accomplish this step. This determination step will estimate the load required to support the half bead  24  around the oil hole  16  such that half bead  24  does not become crushed. Once the load required is estimated, the specific geometry of the support bead  40  may be determined. Accordingly, support bead  40  may be individually tuned to fit a specific application, without resorting to undue experimentation.  
      It is to be understood that the above description is intended to be illustrative and not limiting. Many embodiments will be apparent to those skilled in the art upon reading the above description. The scope of the invention should be determined, however, not with reference to the above description, but with reference to the appended claims with full scope of equivalents to which such claims are entitled.