Abstract:
A gasket for internal combustions is held together by form-locks that do not extend beyond the outer surfaces of the gasket. The form-locks are established in regions where some of the sheets of the gasket do not extend and thus do not incorporate the thickness of those sheets, yet all of the gasket sheets are securely joined.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims benefit under 35 USC 119(e) from the provisional application filed on May 10, 2007 under 35 USC 119(b), which has been assigned patent application No. 60/928,582, which is incorporated by reference in its entirety. 
     
    
     FIELD 
       [0002]    A gasket such as that used for an internal combustion engine is disclosed with multiple sheets interlocked with each other. 
       BACKGROUND 
       [0003]    Gaskets are commonly used to act as a seal between mating mechanical components. A first mechanical component may contain one or more ports or channels that are meant to engage with corresponding ports or channels in a second mechanical part to create a single continuous channel. Typically, such channels transport fluids such as combustion gases and contaminants when used in the environment of an internal combustion engine. For proper performance, the avoidance of accidental leakage of fluids from the channels is desired. Thus, a gasket is typically placed between the mating components and is provided with openings corresponding to the channels to be sealed. When compressed between the mating components, the gasket forms a seal adjacent the openings. 
         [0004]      FIG. 1  shows a prior art gasket for an internal combustion engine. The gasket  20  is formed with a plurality of apertures  22 . These apertures correspond to openings  24  of channels in the engine block; for example, the apertures may correspond to openings for engine cylinder bores, fluid channels, and bolt holes. 
         [0005]    As depicted in  FIG. 2 , the gasket  20  comprises a plurality of sheets such as sheets  26 ,  28 ,  30 . These sheets are arranged as layers, there being a pair of outer sheets  26 ,  28  and at least one or more inner sheets  30 . Preferably the outer sheets  26 ,  28  are formed of steel, however one having skill in the art may choose any suitable alternative material. Materials for the inner sheets  30  may be selected to satisfy desired operational characteristics, for example, a thermally insulating material may be the choice. 
         [0006]    The apertures  22  comprise aligned openings  32  of the sheets  26 ,  28 ,  30  of the gasket  20 . To form a satisfactory seal for openings  24  of a mating component, the individual apertures  22  of each sheet collectively forming an opening  32  must be precisely aligned. In turn, each opening  32  is precisely aligned with a corresponding opening  24 . Even when aligned, the sheets  26 ,  28 ,  30  must be securely joined to maintain this precise alignment. 
         [0007]    One specific gasket that is known is a head gasket, which is disposed between an engine block and a cylinder head of an internal combustion engine. Such a gasket is commonly a steel laminate gasket, including at least two sheets each sheet having apertures aligned with the channels to be sealed. To ensure that a proper seal is formed adjacent the gasket apertures, the sheets of the gasket must be precisely aligned and, once so aligned, securely held together. Additionally, fluid must be prevented from flowing into the regions between the laminate sheets of the gasket itself. 
         [0008]    One common device used to achieve this purpose is an eyelet or grommet as shown in cross-section in  FIG. 3 . An eyelet is a separate part applied to the inner periphery of the aperture and has flanges folded against the outer surfaces of the gasket. The eyelet is applied to the openings in the steel sheets to keep the openings held in alignment and prevent fluid from flowing into the regions between the sheets of the gasket. More specifically,  FIG. 3  depicts a cross-sectional view of an eyelet  34  as known in the art. This separate piece of material is applied at the inner periphery of one of the apertures  22  to mechanically attach the sheets  26 ,  28 ,  30 . The eyelet consists of a cylindrical element  34   a  and a pair of flanges  34   b,    34   c.  The cylindrical element  34   a  extends through the openings  32 , keeping the sheets  26 ,  28 ,  30  aligned and preventing any fluid from flowing into the regions between the sheets. The flanges  34   b,    34   c  hold the sheets together in this alignment. However, the process for making gaskets with these additional eyelet components has several shortcomings as noted above: (1) missing eyelets, (2) inconsistent eyelet dimensions, (3) positional tolerance “stack-up” of eyelet holes causing malformed eyelets, (4) eyelet fragment contamination between sheets, (5) improper ordering of sheets, (6) eyelet component cost, and (7) downtime due to maintenance of eyeleting machines. 
         [0009]    The process for making gaskets with these additional eyelet components has several shortcomings. For example, gaskets are sometimes produced that lack one or more eyelets due to machine error. Additionally, the dimensions of the eyelets may be inconsistent, causing variances in the performance characteristics of the gasket. Another shortcoming is that “positional tolerance stack-up” can result in a malformed eyelet. 
         [0010]    More particularly, as shown in  FIG. 4 , a minimal amount of alignment error Δ 1  may occur between two adjacent sheets that may be too small to detect or prevent and thus may be within the necessary positional tolerances of manufacturing. However the cumulative effect of these errors between several sheets may “stack up” and cause the openings in the outermost sheets to be misaligned by a substantial amount Δ N  causing the resultant eyelets to be misshapen. Further, fragments of eyelet may contaminate the regions between the sheets of the gasket. Yet another shortcoming is that, because corresponding openings in the sheets are identically sized, the sheets to be attached may be improperly ordered when eyeleted. These difficulties may lead to gaskets that are unusable and must be discarded or reworked, thereby incurring additional costs. Further issues include the material and assembly costs associated with the eyelets themselves. Additionally, the machines used to apply the eyelets require periodic maintenance that stalls the manufacturing process. 
         [0011]    An alternative technique for holding the sheets of a gasket securely in proper alignment and providing an effective seal is to machine the sheets so that they mechanically interlock with each other, requiring no additional components. An example of this technique is a form-lock as shown in cross-section in  FIG. 5 . Typically, a first sheet is formed with a flange at the aperture that extends through the second sheet and is folded down against the second sheet. Form-locks can alleviate some of the shortcomings associated with the separate components of eyelets. Additionally, the flange on one of the sheets may serve as a mechanical constraint that prevents or decreases the likelihood of the sheets from being assembled in an improper order (“poka-yoke”). However, this technique is still sensitive to positional tolerance stack-up if several layers are joined by the forn-lock. 
         [0012]    More specifically,  FIG. 5  depicts a cross-sectional view of a form-lock  40  as another means for securely joining multiple sheets  26 , 28 ,  30 . One of the outer sheets  28  additionally comprises a flange  42  that extends from the periphery of the opening  32 . The flange  42  has a cylindrical portion  42   a  that extends through the openings  32  in the remaining sheets  26 ,  30  and a flat portion  42   b  that is folded back against the outer sheet  26 . This form-lock structure  40  securely attaches the sheets  26 ,  28 ,  30  through a mechanical interlock without the need for extra components and the surface of the cylindrical portion of the flange  42   a  provides a sealing surface to prevent fluid from flowing into the regions between the sheets. 
         [0013]    Apart from manufacturing concerns, prior art approaches also suffer from operational shortcomings. As known in the art, a final aperture structure protrudes beyond the outer surfaces of the gasket sheets. For example, as shown in  FIGS. 3 and 5 , eyelets  34  and form-locks  40 , protrude beyond the planes  36 ,  38  defined by the outer surfaces of the gasket. This is undesirable because the gaskets are typically used under high pressures and the protrusion results in uneven application of this pressure. This uneven pressure may cause premature wear on the gasket (e.g., exacerbate stress in a localized region) or potentially create poor sealing conditions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The features and advantages of the present gasket will be apparent from the following description, taken in conjunction with the accompanying drawings, in which 
           [0015]      FIG. 1  is a view of a prior art cylinder head gasket and engine block with corresponding openings for cylinder bores and fluid channels; 
           [0016]      FIG. 2  is an exploded view of a prior art sheet metal gasket depicting a plurality of sheets including two outermost sheets and several inner sheets disposed between the outermost sheets; 
           [0017]      FIG. 3  is a cross-sectional view of a prior art eyelet arrangement for joining the sheets of a gasket at an aperture therein; 
           [0018]      FIG. 4  is a cross-sectional view of a prior art eyelet arrangement for joining the sheets of a gasket at an aperture therein depicting the effects of positional tolerance stack-up; 
           [0019]      FIG. 5  is a cross-sectional view of a prior art form-lock arrangement for joining the sheets of a gasket at an aperture therein; 
           [0020]      FIG. 6  is a cross-sectional view of an aperture in a gasket according to a first exemplary embodiment; 
           [0021]      FIGS. 7A-C  comprise a series of three cross-sectional views of an aperture in a gasket according to the first embodiment, showing the procedural steps involved in forming the improved form-lock; 
           [0022]      FIGS. 8A-B  comprise cross-sectional views of two apertures in a gasket having a form-lock according to a second exemplary embodiment; and 
           [0023]      FIG. 9  is a cross-sectional view of an aperture in a gasket having a form-lock according to a third exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    A first example of an improved gasket  120  is illustrated in  FIGS. 6 and 7 . A metallic form-lock  144  is used to join outer metallic sheets  126 ,  128  of the gasket  120 . Each of sheets  126 ,  128  include an outer surface  131 , an inner surface  132 , and at least one opening  134  formed therein. One or more inner sheets are disposed between sheets  126 ,  128 , each inner sheet including at least one opening  135  formed therein in alignment with opening  134 . The form-lock  144  is restricted to a region in which the inner sheets  130  do not extend between the outer sheets  126 ,  128 . So long as the combined thickness of inner sheets  130  is at least as thick as outer sheet  128 , form-lock  144  will be no thicker than the gasket  120  and can therefore be located so that it does not protrude beyond the planes  136 ,  138  defined by the outer surfaces of the gasket, being disposed within planes  136 ,  138 . 
         [0025]    As shown in  FIG. 7 , one method of establishing form-lock  144  is to form material from the outer sheets  126 ,  128 . In  FIG. 7   a,  a first extrusion  148 , formed by interaction of a male punch and a female die (not shown), extends from the periphery of the opening in the first sheet  126  a sufficient distance so that the flange of the form-lock  144  will not overlap with the inner sheets  130 . In  FIG. 7   b,  a second extrusion  150  extends from the periphery of the opening in the second outer sheet  128  beyond the first extrusion  148  and through the aperture  134 . As shown in  FIG. 7   c,  the second extrusion  150  is then folded back over the first extrusion  148 . The only sheet within the flange of the second extrusion  150  is the extrusion  148  of the first outer sheet  126 . The thickness of the form-lock  144  is therefore equal only to the thickness of sheet  126  added to twice the thickness of sheet  128 . Therefore in this embodiment, as long as the inner sheets  130  are at least as thick as the outer sheet  128 , the resulting form-lock  144  is no thicker than the rest of the gasket  120  and can be confined within the planes  136 ,  138  defined by the outer surfaces of the gasket. Because form-lock  144  envelops only two sheets, the problems caused by positional tolerance stack-up are attenuated. If the extrusions are achieved before the sheets are placed together they may serve as a fail-safe or mistake proof device to ensure that a proper ordering of the sheets. Because the inner sheets  130  do not experience uneven stresses and are not exposed, they can be formed of a broader range of materials. For example, a non-metallic thermally insulating material can be selected for the inner sheets  130 . 
         [0026]    In an alternative embodiment of a gasket  220  shown in cross-section in  FIG. 8 , at least two form-locks  252 ,  254  are established in the gasket  220  at different locations. These form locks are formed from formed material as described in connection with the first embodiment and join respectively different pairings of sheets. For example, as shown in  FIG. 8   a,  a first form-lock  252   a  attaches the outer sheet  226  to the inner sheet  230 . This first form-lock formed of material formed from the layers  226 ,  230  so that it does not overlap with the remaining layers (in this example, outer layer  228 ) in a similar manner to that shown in  FIG. 7 . The thickness of the form-lock is therefore only as great as the outer sheet  226  added to twice the thickness of inner sheet  230 . A second form-lock  254   a  similarly attaches the inner sheet  230  with the outer sheet  228 . This second form-lock  254   a  is similarly formed of material formed from the layers  226 ,  230  so that its thickness is only as great as the inner sheet  230  added to twice the thickness of outer sheet  228 . The resultant gasket  220  has three sheets  226 ,  228 ,  230  joined with each other while each individual form-lock  252   a,    254   a  respectively joins only two sheets and is no thicker than the gasket  220 . Additional sheets can be securely attached to the gasket with similar form-locks without requiring any increase in individual form-lock thickness. This alleviates some of the uneven stresses that would be caused by previously known attachment methods as well as problems associated with positional tolerance stack-up. 
         [0027]    As shown in  FIG. 8   b,  the direction of these form-locks  252   b,    254   b  can be adjusted so that the flanges respectively extend from the outer sheets  226 ,  228  through the inner sheet  230 . In this configuration of the second embodiment the form-locks  252   b,    254   b  are confined within the planes  236 ,  238  defined by the outer surfaces of the gasket  220  so long as the outer sheets  226 ,  228  are of the same thickness. This configuration further reduces uneven stresses on the apertures of gasket  220 . 
         [0028]    Because the form-locks  244  of this embodiment envelop a reduced number of sheets, the problems caused by positional tolerance stack-up are attenuated. If the extrusions are achieved before the sheets are placed together they may serve as a fail-safe or a mistake proof device to ensure a proper ordering of the sheets. 
         [0029]    Referring now to  FIG. 9 , yet another embodiment of a gasket  320  present invention is depicted. In this embodiment, a metallic form-lock  344  is used to join outer metallic sheets  326 ,  328  of the gasket  320 . Each of sheets  326 ,  328  include an outer surface  331 , an inner surface  332 , and at least one opening  334  formed therein. 
         [0030]    One or more inner sheets  330  are disposed between sheets  326 ,  328 , each inner sheet  330  including at least one opening  335  formed therein in alignment with opening  334 . The form-lock  344  is restricted to a region in which the inner sheets  330  do not extend between the outer sheets  326 ,  328 . So long as the combined thickness of inner sheets  330  is at least as thick as outer sheet  328 , form-lock  344  will be no thicker than the gasket  320  and can therefore be located so that it does not protrude beyond the planes  336 ,  338  defined by the outer surfaces of the gasket, being disposed within planes  336 ,  338 . 
         [0031]    One method of establishing form-lock  344  is to form material from the outer sheets  326 ,  328 . A first extrusion  348 , formed by the interaction of a male punch and a female die (not shown), extends beyond the opening  335  in the inner sheet  330  a sufficient distance so that the form-lock  344  will not overlap with the inner sheet  330 . 
         [0032]    The first extrusion  348  has a first portion  360  angled toward the outer sheet  328 . A second portion  362  of the first extrusion  348  extends substantially parallel to the outer sheet  328 . A second extrusion  350 , formed in a similar manner to the first extrusion  348 , extends beyond the opening  335  in the inner sheet  330 . The second extrusion  350  is then folded back over the first extrusion  348 . 
         [0033]    The only sheet within the second extrusion  350  is the first extrusion  348 . The thickness of the form lock  330  is therefore equal only to the thickness of the first outer sheet  326  added to twice the thickness of the sheet  328 . Therefore, in this embodiment, as long as the inner sheets  330  are at least as thick as the outer sheet  328 , the resulting form-lock  344  is no thicker than the rest of the gasket  320  and can be confined within the planes  336 ,  338  defined by the outer surfaces of the gasket. 
         [0034]    Based on the foregoing, it can be appreciated that if the gasket needs to be disassembled or the form locks need to be re-worked, that only the layers of the form lock may be impacted. Thus, the layers not forming the form lock are preserved in substantially their original state. 
         [0035]    It can also be appreciated that any of the form locks disclosed herein can be used on the same gasket with any of the other forms locks disclosed herein to have locking devices that are easier to locate and/or manufacture in particular places in the gasket and/or to employ a particular lock at a particular location on the gasket based on the effectiveness and/or characteristics of the lock. 
         [0036]    The preferred embodiments described are exemplary only and not meant to be restrictive beyond the express limitations of the appended claims. Descriptive labels such as “outer sheet” are for illustrative purposes of the exemplary embodiments and are not meant to exclude embodiments consisting of more or fewer sheets than disclosed herein. Modifications or alterations may be made to the disclosed embodiments without departing from the scope of the following claims.