Abstract:
A process for fabricating a metallic sheet containing at least one raised surface zone. The process including the steps of making at least one cutout ( 20 ) in said metallic sheet ( 10 ) to obtain at least one flap ( 22 ), subjecting the said at least one flap ( 22 ) to deformation with bending and extension so as to form an overlap, and flattening and calibrating the protruding height of said at least one flap ( 22 ) to form a raised surface zone ( 24 ) of adjusted

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of French Patent Application 04 52117, filed Sep. 21, 2004. The disclosure of the above application is incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a process for fabricating a metallic sheet with at least one integrated raised surface zone for a compressed metallic gasket such as a cylinder head gasket, and to a gasket including at least one metallic sheet provided with at least one raised surface zone that makes it possible to create a gasket.  
       BACKGROUND OF THE INVENTION  
       [0003]     It is known that in the case of compressed metallic gaskets such as cylinder head gaskets, particularly in the case of the sheet of a single-sheet gasket or one of the active sheets of a multi-sheet gasket, the stress zones are located around the tightening points.  
         [0004]     These zones are thus relatively concentrated and cause differences in the distribution of applied pressures. As such, possible tightness differences occur in certain zones.  
         [0005]     One solution to this problem consists of increasing the tightening pressures. Such a solution, however, is generally not satisfactory because the difference in pressures subsists. Moreover, an increase in tightening pressures requires a resizing of the parts which is contrary to the goals generally pursued by the automobile industry, at least in terms of light weight.  
         [0006]     Thus, to re-establish a distribution equilibrium, it is known to use stops. These stops pick up the stresses in certain distinct zones of tightening points to homogenize the charting or tightening pressures.  
         [0007]     Although many approaches have been proposed to create these stops, they are not all satisfactory, particularly from the cost perspective. In fact, gaskets equipped with such stops must give convincing results in terms of equilibrium distributions of tightening stresses, and must be capable of being fabricated rapidly, inexpensively, and with satisfactory reproducibility.  
         [0008]     It is also known in the industry that the recovery of parts for complementary fabrication steps is highly penalizing from the standpoint of management, and particularly because it causes major cost increases.  
       SUMMARY OF THE INVENTION  
       [0009]     In view of the above drawbacks, an object of the present invention is to obtain stops directly and continuously on the fabrication line for a single-sheet gasket or one of the sheets of a multi-sheet gasket.  
         [0010]     Another object is to obtain on the same sheet or the same plate, stops of different thicknesses depending on the zone to obtain a charting of pressures, and not only of distribution points. In this case, the stops are mostly on the surface and, hence, will in the following be referred to by the term “raised surface zone.” 
         [0011]     Another objective of the invention is to be able to obtain, after tightening, the desired pressure charting and thus to provide raised surface zones appropriately distributed to obtain this charting. To obtain such a distribution, it is necessary to have multiple raised surface zones, which explains the interest in simple fabrication such as that based on the present invention.  
         [0012]     The fact that the pressure stresses can be better distributed also results in less deformation of the parts that compress the gasket on both sides. As a result, it is possible to reduce the dimensions of these parts or their complexity needed to respond to such deformations.  
         [0013]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     This description will be made by reference to the attached sets of drawings of which:  
         [0015]      FIG. 1  shows a view of a sheet of a metallic sealing gasket according to a principle of the present invention;  
         [0016]      FIGS. 2A, 2B , and  2 C show views of steps in the fabrication of raised surface zones of the invention for a sealing gasket such as that of  FIG. 1 ;  
         [0017]      FIG. 3  shows a greatly enlarged detailed view of a raised surface zone; and  
         [0018]      FIGS. 4A  to  4 F show a view of different cutout profiles for obtaining the raised surface zones of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0020]      FIG. 1  shows a sheet  10  of a single-sheet gasket, or one of the active sheets in the case of a multi-sheet gasket. In the following description, the term “sheet” will be used to refer indifferently to a metallic sheet of a single-sheet gasket or to one of the sheets in the case of a multi-sheet gasket, particularly the intermediate sheet, generally made of a more malleable carbon steel.  
         [0021]     For application to a cylinder head gasket, the sheet  10  preferably has a thickness of, for example, 0.01 to 1.0 millimeters.  
         [0022]     Also in the following description, it should be understood that although a cylinder head gasket is mentioned as an example of the present invention, the present invention can be used in applications that extend to gaskets for exhaust lines, gaskets for receivers, or more generally to peripheral gaskets.  
         [0023]     Sheet  10  generally comprises central cutouts  12  that correspond to cylinders and holes  14  and  16 , respectively, for the passage of water and oil. Also provided are passages  18  for bolts that are used to tighten two parts, namely in the case of a cylinder head gasket, the engine block and the cylinder head.  
         [0024]     The process of the present invention consists of forming at least one cutout  20  in the sheet  10  to obtain a flap  22 . The cutout  20  is a partial cutout to allow the resulting flap  22  to bend along a line that is not cut. The cutout  20  and bent flap  22  are shown in  FIG. 2A . It has a length L and a profile coupled to that of the cutout  20 .  
         [0025]     A second step of fabrication of the raised surface zone of the invention consists of extending the flap  22 . The extension of the flap  20  can be accomplished, for example, by forging. This extension ΔL remains limited and is preferably made at a free end of the flap  22 .  
         [0026]     A third step consists of flattening and simultaneously calibrating a protruding height of the flap  22  to obtain an adjusted raised surface zone  24 . Calibration is achieved by pressing the flap  22  so that it tends to retake its place in the cutout  20  from which it was formed.  
         [0027]     Because of the extension ΔL, a reintegration of the flap  22  into the cutout  20  is not possible. Such an action leads to an overlap with superposition of the end of flap  22  on the edge of the cutout  20  forming an extra height h which, during mounting, constitutes the desired raised surface zone  24 . The flattening and calibration stresses make it possible to obtain the desired height.  
         [0028]     For the sheet  10  to be used as an element of a gasket, the calibration stresses must be lower than the subsequent tightening stresses on the sheet  10 . In this manner, the resulting raised surface zone  24  will be resistant to crushing stresses.  
         [0029]     This raised surface zone  24  is shown in detail in  FIG. 3 . Under the calibration stresses, the edges of the cutout  20  and the end of the flap  22  yield and undergo a deformation to form an essentially tapered interface  26 .  
         [0030]     To give an order of magnitude, the cutouts  20  and the flaps  22  derived therefrom have dimensions of about 0.5 to 5 millimeters.  
         [0031]     It should be understood that calibration and flattening tools can have profiles that are not flat, which can generate different calibrations that results in raised surface zones having different heights h. These height variations make it possible to generate a surface charting and not just a point charting.  
         [0032]     The distribution of pressures is very gradual and almost continues over the entire surface without generating points of constraint.  
         [0033]     The density of the raised surface zones  24 , their dimensions, height, and localization on the surface allow very fine regulation of the distribution. As can be seen in  FIG. 4 , the shapes of the cutouts  20  and, hence, of the flaps  22 , are long or short, curvilinear, oblong, rectangular, triangular, or circular.  
         [0034]     These profiles are retained depending on the zone and on the available space in this zone.  
         [0035]     The profiles on a given sheet can be different.  
         [0036]     Each metallic sheet can undergo the different steps of the continuous process on the same production line. The gasket thus obtained and provided with at least one sheet  10  with at least one raised surface zone  24  obtained by the process of the invention is simple and perfectly reproducible once the tools have been adapted because there is no other external intervention that would cause variation of the different parameters.  
         [0037]     More particularly, such a process is applicable in the case of metallic cylinder head gaskets, such as a single-sheet gasket and the intermediate sheet of a multi-sheet gasket.  
         [0038]     According to a variant of the present invention, it is possible to provide, for example at the end of the flap  22 , at least one rib at the same time as the extension.  
         [0039]     This also makes it possible to obtain a raised surface zone  24  and to increase the number of ways in which to respond to problems that could turn out to be quite complicated, particularly in the case where the material of which the sheet  10  is made is only slightly malleable, such as stainless steel which constitutes the single-sheet gaskets.  
         [0040]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.