Patent Publication Number: US-7900280-B2

Title: Goggles

Description:
This invention relates to goggles, and particularly but not exclusively to sports goggles, e.g. swimming goggles. 
     Conventional swimming goggles have two lens cups. Each lens cup includes a rearwardly-directed peripheral seal portion which is adapted to seal against the wearer&#39;s face to enclose the space behind the lens cup. The lens cups are connected to one another at their medial sides (the sides adjacent the wearer&#39;s nose) by a bridging section that is adapted to extend across the wearer&#39;s nose. A head strap is fixed to the lateral sides of the lens cup (the sides adjacent the wearer&#39;s ears) and is adapted to extend round the back of the wearer&#39;s head to hold the goggles in position. 
     Commonly, the seal portion is an annular foam pad. The foam pad is designed to distort to conform to the wearer&#39;s face, under pressure applied to the pad via the head strap. The head strap must be tight to achieve an effective seal between the pad and the wearer&#39;s face, which can cause discomfort to the wearer. 
     As a common alternative to the foam pad, an annular flexible rubber flange is often used as a seal portion, extending obliquely from the rim at a generally uniform angle relative to peripheral walls of the lens cup. This seal is sometimes known as a gasket-type seal. This flange is designed to distort substantially to conform with the wearer&#39;s face by expelling air from the space behind the lens cup upon contact with the wearer&#39;s face. The air expulsion creates a suction-effect, causing the seal portion to press against the wearer&#39;s face, ensuring adequate sealing. 
     However, the suction force required to ensure adequate sealing can cause substantial discomfort to the wearer. This is evidenced by the red marking normally visible around the wearer&#39;s eye sockets after removal of the goggles. The red marking results from distortion to the facial tissue and subcutaneous musculature. 
     It is a general proposition of the present invention to provide a seal portion for a goggle lens cup which is preshaped or preformed to conform substantially with a wearer&#39;s face (i.e. it does not rely on any significant pressure against the face to give its conforming shape). Accordingly, little force may be needed to seal the lens cup adequately with the wearer&#39;s face since significant distortion of the seal portion and/or the wearer&#39;s face to obtain an adequate seal may not be necessary. 
     According to a first aspect of the present invention there is provided:
         goggles, comprising:   a lens cup having a peripheral rear edge,   a seal portion extending around the peripheral rear edge, adapted to seal against a wearer&#39;s face, wherein   the seal portion has a face contact surface preformed to follow substantially the contours of the wearer&#39;s face around the wearer&#39;s eye socket.       

     Preferably, the profile of the wearer&#39;s face around the wearer&#39;s eye socket is in the region adjacent the maxilla, zygomatic and frontal bone arches, adjacent to the eye socket, and the side of the nasal bone where the nasal bone meets the frontal and maxilla bones. 
     The term ‘preformed’ is used to indicate that the face contact surface is shaped to follow substantially the contours of a wearer&#39;s face around the wearer&#39;s eye socket prior to any contact with the face. The face contact surface is the surface of the seal portion that contacts the face when the goggles are worn. 
     The seal portion may be formed integrally with the lens cup, e.g. it may be the peripheral rear edge (rim) of the lens cup itself. By having a seal portion integral with the lens cup, manufacture of the goggles is simplified. Furthermore, the goggles may be more resilient, since there are fewer parts that can come apart undesirably. Also, they may be less bulky, reducing the amount by which they project forward of the brow when worn, potentially improving the hydrodynamics. 
     Alternatively, the seal portion may be a separate element fitted to the peripheral edge of the lens cup, such as a gasket or a pad. The gasket may be rubber and may lie flat against the peripheral rear edge of the lens cup, following the contours of the rear edge. Preferably, the pad is filled with a viscous fill substance such as a gel or gel-like fill substance. The pad seal portion may have a generally U-shaped cross section, with the fill substance being contained in the cavity formed by the U-shape and the peripheral rear edge of the lens cup. The base of the U-shape is provided by the face contacting surface. The U-shaped seal is less prone to creasing than a tubular seal portion. Nevertheless, alternatively, the seal portion may be tubular. Accordingly, it may have a cross-section that is generally circular, elliptical, or polygonal etc. Thus, a complete cavity containing the fill substance may be provided by the seal portion. Preferably, the peripheral rear edge of the lens cup is contoured in a similar or identical manner to the face contact surface of the pad seal portion, so that the depth of the cavity may remain substantially the same around the entire peripheral rear edge. This may make construction simpler. 
     When the seal portion is a gasket or a pad in particular, the seal portion may be resiliently deformable. Accordingly, if the face contact surface of the seal portion does not conform exactly to the wearer&#39;s face contours, the difference can be accommodated by some deformation of the seal portion. If the peripheral edge of the lens cup provides the seal portion, and this peripheral portion is rigid, the difference may be accommodated by distortion of the wearer&#39;s facial tissue. However, since the face contact surface is preformed to follow substantially the contours of the wearer&#39;s face, this distortion will be minimal, and may be much less than in conventional goggles. Accordingly, relatively low contact forces are required between the seal portion and the wearer&#39;s face in order to effect an adequate seal. Thus, discomfort to the wearer may be reduced; the distortion of the tissue and subcutaneous musculature around the eye socket of the wearer is minimised, reducing the likelihood of any reddening of the face. Since high contact forces are not necessary, the tension of a head strap, for holding the goggles to a wearer&#39;s face may be kept relatively low. 
     The seal portion may comprise a flange. The flange may project from the face contact surface. The flange may extend right around the face contact surface, or just a part of the face contact surface. Preferably, the flange is resiliently deformable, e.g. is formed of rubber material, so that it may deform on contact with the face. The flange may be particularly advantageous when the peripheral edge of the lens cup provides the face contact surface, since it may add some deformability to an otherwise rigid seal portion, improving its sealing properties. Nevertheless, the flange may be much smaller than in conventional goggles, and may provide merely an auxiliary sealing feature to the seal portion, to improve further its sealing properties. 
     The contact surface of the seal portion may be preformed to follow the facial contours of the ‘average’ wearer. However, since the facial structure of persons can vary significantly between different demographic groups, e.g., based on their ethnic background, gender and age etc., preferably, the face contact surface of the seal portion is preformed to follow substantially the average contours of a wearer&#39;s face belonging to a specific demographic group. Accordingly, numerous goggles variants according to the present invention may be provided, each for a different demographic group, such as Caucasian adult male, African adult female, Chinese child male etc. Thus, assuming that the correct seal portion is used by a wearer for their demographic group, the need for any deformation of the seal portion and/or the wearer&#39;s face, to effect adequate sealing, may be minimised. 
     Alternatively, the face contact surface may be preformed bespoke to the wearer. To achieve this, moulds of the wearer&#39;s face etc. may be taken prior to manufacture. 
     Since the face contact surface is preformed to follow substantially the contours of a wearer&#39;s face around the wearer&#39;s eye socket, adjustment of the seal portion in order to locate in the correct position of the wearer&#39;s face, may be minimised. Furthermore, since the face contact surface is preformed to substantially follow the contours of a wearer&#39;s face around the wearer&#39;s eye socket, the seal portion may have a relatively small depth, e.g. less than 10 mm, or even less than 5 mm depth. Accordingly, the seal portion need not obscure substantially the wearer&#39;s field of view. Still furthermore, the nature of the geometry of the face contact surface is such that moulding of the seal portion, and/or lens cup may be performed easily, without the need for any re-entrant angles. 
     To aid a more detailed description of the seal portion, ‘x-’, ‘y-’ and ‘z-directions’ of the lens cup/seal portion/face contact surface, and different regions of the seal portion will now be defined. The z-direction is perpendicular to the best-fit plane of the contact surface (defined below). When the lens cup is worn, the z-direction runs, generally, in a direction normal to the surface of the centre of the pupil of the wearer&#39;s eye. The zero point of an axis along the z-direction is located on the best-fit plane, and the positive side of the axis extends toward the eye of the wearer, in use, and the negative side extends away from the wearer&#39;s eye, in use. The x-and y-directions lie, perpendicular to each other, along the best fit plane of the contact surface (and hence perpendicular to the z-plane). When the lens cup is worn by a wearer with head upright, the x-direction runs generally horizontally across the wearer&#39;s face, and the y-direction runs generally vertically, up and down the wearer&#39;s face. 
     For the purposes of this description, the seal portion is divided up into four regions: a medial region, a lateral region, a top region and a bottom region. The medial region is a part of the seal portion which, when worn, is adjacent the wearer&#39;s nose. The medial region is situated at the medial end of the seal portion. The lateral region is located at the opposite side of the seal portion from the medial region, in the x-direction, and is a part of the seal portion, which, when worn, is nearest the wearer&#39;s ears. The lateral region is situated at the lateral end of the seal portion. The upper region, and the lower region, are the parts of the seal portion positioned intermediate the lateral and medial regions and which, when worn, are nearest the top of the wearer&#39;s head and the wearer&#39;s chin respectively. 
     To aid understanding,  FIG. 1  shows an example face contact surface  11  of the seal portion  1  of a lens cup according to present invention situated in position adjacent the eye socket of a wearer&#39;s face  2 . The x-, y-, and z-directions are marked in  FIG. 1  along with the medial region  12  (indicated by dotted-circle  12 ), lateral region  13  (indicated by dotted circle  13 ), upper region  14 , lower region  15 , medial end  16  and lateral end  17  of the seal portion.  FIG. 2   a  shows an even distribution of points  21  over the face contact surface. The best-fit plane  22  is calculated as a best-fit plane through these points  21 , as shown in  FIG. 2   b.    
     The central axis of the contact surface is a line which runs along the centre of the contact surface as it extends around the peripheral edge of the lens cup. In this description, the width of the face contact surface at a particular position is taken to be the distance between the sides of the face contact surface in a direction perpendicular to the central axis, at that position. (The dotted line  23  in  FIG. 1  indicates the central axis  23  of the face contact surface  11  of  FIG. 1 , and the width at a sample position of the face contact surface is indicated by arrow  24 ). 
     Preferably, the width of the face contact surface is greater at the medial and/or lateral regions than at the upper and lower regions. 
     A wider face contact surface is generally more compliable. This is particularly advantageous at the medial region, since the medial region will normally contact the wearer&#39;s face adjacent the nasal bone. This part of the face is relatively firm, i.e. non-compliable, and is likely to vary significantly from one wearer to the next. By having a relatively compliable contact surface, any differences between the actual wearer and e.g. the ‘average’ wearer for which the seal portion is designed, may be accommodated more easily, and an adequate seal effected. Preferably, the width of the face contact surface is from 5 mm to 9 mm at the medial region. 
     A relatively wide face contact surface is desirable at the lateral region since, normally, contact forces applied to the face by the lateral region of the face contact surface are relatively low. By having a wide contact surface, better sealing is achieved between the contact surface and the face, despite the low contact forces at this point. Forces are normally lower at this position than elsewhere since, at this position, the dominant force applied to the seal portion is from a head strap of the goggles and the dominant force acts in a direction substantially perpendicular to the direction of contact between the seal portion and the wearer&#39;s face. Preferably, the width of the face contact surface is from 8 mm to 12 mm at the lateral region. 
     Preferably, the ratio of the spatial extent of the face contact surface in the x-direction to the spatial extent of the face contact surface in the y-direction is between 1.4 and 1.5. Preferably, the maximum distance between the upper region and the lower region of the contact surface, in the y-direction is 50 mm. Accordingly, interference between the lens cup and the natural movement of the eye and eye lid when worn, may be minimised or even eliminated. 
     Preferably, the face contact surface curves in the z-direction as it extends from the medial to the lateral end generally in the x-direction. Preferably, the range of deviation of the contact surface from the best-fit plane of the contact surface in the z-direction, as it curves, is at least 2 mm, more preferably at least 3 mm, even more preferably at least 5 mm either side of the best-fit plane. Preferably, the total deviation in the z-direction is at least 5 mm, more preferably at least 10 mm. This degree of curvature enables the face contact surface to follow substantially the contours of the wearer&#39;s face. 
     Preferably, the local plane (rather than the best fit plane) of the face contact surface has an angle at the medial region  42  and the lateral region  43  of between 30 and 60 degrees relative to the xy-plane. Accordingly, the face contact surface may face in generally the same direction in the medial and lateral regions. Preferably, the local plane of the face contact surfaces at the upper and lower regions has a shallower angle relative to the xy-plane than at the medial and lateral regions. In fact, the plane at the upper and lower regions may approach or reach a zero-degree angle relative to the xy plane, so the plane may be substantially parallel to the xy-plane at these points. 
     The face contact surface of the seal portion may be joined to the rest of the lens cup via side walls of the seal portion, or, if the seal portion is integral with the lens cup, as described above, the face contact surface may be joined directly to side walls of the lens cup. Preferably, a smooth transition is provided between the contact surface and the side walls. To facilitate the smooth transition, curved corner portions may be provided at the interface between the face contact surface and the side walls. Alternatively, the face contact surface may blend into the sidewalls so that there are no corner portions. A smooth transition improves comfort for the wearer. Preferably, at the medial region of the face contact area, the radii of the curved corners are between 1.2 mm and 3 mm. A smooth transition is particularly important at the medial region, since the contact force between the contact surface and the wearer&#39;s face is relatively high at this position as described above, and any sharp edges at the interface between the face contact surface and the sidewalls would be very noticeable to the wearer. 
     According to a second aspect of the present invention, there is provided:
         goggles, comprising:   a lens cup having a peripheral rear edge,   a seal portion extending around the peripheral rear edge, adapted to seal against a wearer&#39;s face, wherein   the seal portion has a face contact surface the orientation of which changes continuously in two or more of the x-, y-and z-directions of the lens cup as it extends around the peripheral rear edge of the lens cup.       

     One or more features of the first and second aspects of the present invention may be combined. 
     The orientation of the face contact surface may change in two of the x-, y-and z-directions around a part of the peripheral read edge, and a different two of the x-, y-and z-directions around another part of the peripheral rear edge. For example, the orientation of the face contact surface may change in the x-and z-directions as it extends around part of the peripheral rear edge, whereas it may change in the y-and z-directions as it extends around another part of the peripheral rear edge. 
     Furthermore, the orientation of the face contact surface may change in two of the x-, y-and z-directions around a region of the peripheral rear edge, and all three x-, y-and z-directions around another region of the peripheral rear edge. For example, the orientation of the face contact surface may change in the x-, y-and z-directions as it extends around part of the peripheral rear edge, whereas it may change in only the y-and z-directions as it extends around another part of the peripheral rear edge. 
     Preferably, the orientation of the face contact surface changes continuously in all of the x-, y-and z-directions. 
     By continually changing orientation in two or all of the x-, y-and z-directions, the contact surface may follow substantially the contours of the wearer&#39;s face. 
     Preferably, the lens cup has curvature in the x-, y-and z-directions. This may reduce the level of hydrodynamic drag when used, improving performance. 
     According to a third aspect of the present invention, there is provided a seal portion for goggles substantially as described with respect to the first and second aspects of the present invention. 
    
    
     
       Embodiments of the present invention are now described with reference to the accompanying drawings, in which: 
         FIGS. 1  show the position of a face contact surface of a seal portion according to the present invention relative to a wearer&#39;s face; 
         FIG. 2   a  and  2   b  indicate how the best-fit plane of the face contact surface according to present invention is determined; 
         FIG. 3  shows a front oblique view of goggles according to a first embodiment of the present invention; 
         FIG. 4  shows a rear oblique view of the goggles of  FIG. 3 ; 
         FIG. 5   a  and  5   b  show a shaded rear and side view respectively of the seal portion of the goggles of  FIG. 3 ; 
         FIG. 6   a  and  6   b  show a line rear and side view respectively of the seal portion of the goggles of  FIG. 3 ; 
         FIGS. 7   a  and  7   b  show a shaded rear and side view respectively of a seal portion for goggles according to a second embodiment of the present invention; 
         FIGS. 8   a  and  8   b  show a line rear and side view respectively of the seal portion of  FIGS. 7   a  and  7   b;    
         FIGS. 9   a ,  9   b  and  9   c , show sectional views of the lateral, medial, and upper regions respectively of the seal portion of  FIGS. 7   a  and  7   b;  and 
         FIGS. 10   a ,  10   b  and  10   c  show a side oblique view, rear view and top view respectively of a seal portion integral with a lens cup according to a third embodiment of the present invention. 
     
    
    
     Goggles  3  according to a first embodiment of the present invention are shown in  FIG. 3 . The goggles comprise two lens cups  31 . The lens cups  31  are connected to each other at their medial sides  32  by a nose bridging section  33  that is adapted to extend across the wearer&#39;s nose. A head strap  34  is fixed to connection portions  34  at the lateral sides  36  of the lens cups  31  and is adapted to extend round the back of the wearer&#39;s head to hold the goggles  3  in position. 
     Referring now to  FIG. 4 , each lens cup  31  includes a rearwardly-directed peripheral seal portion  4  which is adapted to seal against the wearer&#39;s face to enclose the space behind the lens cup  31 . The seal portions  4  are generally elliptical, and are connected to, and extend around, the peripheral rear edge of the lens cups  31 . 
     In this embodiment, the seal portions have a generally U-shaped cross section, with fill substance being contained in a cavity formed by the U-shape and the peripheral rear edge of the lens cups  31 . The fill substance is a gel, making the seal portion  4  resiliently deformable and giving good cushioning properties. 
     The seal portion  4  of each lens cup  31  has a face contact surface  41 , designed to contact the wearers&#39; face, generally around the wearer&#39;s eye socket, in use. The seal portion  4  is shaped to follow the contours of the wearer&#39;s face at the points of contact with the face. In particular, it is designed to follow the contours of the face over the zygomatic and frontal bone arches, and the side of the nasal bone. By having this ‘preformed’ shape, little or no distortion of the seal portion may be required for adequate sealing with the wearer&#39;s face. The peripheral rear edge of the lens cup  31  is contoured similarly to the face contact surface  41 . 
     The orientation of the face contact surface  41  changes continuously as it extends around the peripheral rear edge of the lens cup  31 , in two or three of the x-, y-and z-directions. 
     As can be seen in  FIGS. 5   a  and  6   a , the angles of the face contact surface  41 , across the width of the face contact surface  41 , at the medial end  46  of the medial region  42  and at the lateral end  47  of the lateral region  43  are similar. Essentially, at these positions, the face contact surface faces in generally the same direction, with angles relative to the xy-plane of between 30 and 60 degrees. A smooth transition of the face contact surface orientation occurs between these medial and lateral regions,  42 ,  43  over the upper and lower regions  44 ,  45  of the face contact surface  41 . 
     In particular, as the face contact surface  41  extends from the medial region  42  to the lateral region  43 , via the upper region  44 , the local plane (rather than the best fit plane) of the face contact surface  41  rotates anti-clockwise about the z-axis. As it rotates, the angle or slant of the plane changes from the 30 to 60 degree angle relative to the xy-plane at the medial region  42 , towards zero degrees relative to the xy-plane (i.e. towards a position where it is, or is almost, parallel to the xy-plane) in the upper region  44 , and back to the 30 to 60 degree angle relative to the xy-plane at the lateral region. Whereas, as the face contact surface  41  extends from the medial region  42  to the lateral region  43 , via the lower region  44 , the local plane of the face contact surface  41  rotates clockwise about the z-axis. As it rotates, the angle or slant of the plane changes from the 30 to 60 degree angle relative to the xy-plane at the medial region  42  mentioned above, towards zero degrees relative to the xy-plane (i.e. towards a position where it is, or is almost, parallel to the xy-plane) at the lower region  45 , and back to the 30 to 60 degree angle in the xz plane at the lateral region  43 . 
     The width of the face contact surface  41  is greater at the medial and lateral regions  42 ,  43  of the face contact surface  41  than at the upper and lower regions  44 ,  45  of the face contact surface  41 . 
     The width of the face contact surface  41  at the medial region  42  is approximately from 5 mm to 9 mm. A wide face contact surface  41  is desirable at the medial region  42  since, normally, contact forces applied to the face by the medial region  42  are relatively high. By having a wide face contact surface  41 , the forces are distributed more evenly to the wearer&#39;s face, reducing discomfort and the possibility of reddening of the wearer&#39;s face. Forces are normally higher at this position than elsewhere since, at this position, the dominant force applied to the seal portion  4  is via the nose bridging section  33  of the goggles  3 , which pulls the seal portion  4  directly toward the nasal bone of the wearer. 
     The width of the face contact surface  41  at the lateral region  43  is approximately from 8 mm to 12 mm. A wide face contact surface  41  is desirable at the lateral region  43  since, normally, contact forces applied to the face by the lateral region  43  are relatively low. By having a wide face contact surface  41 , better sealing is achieved between the face contact  41  surface and the face, despite the low contact forces at this point. Forces are normally lower since, at this position, the dominant force applied to the seal portion  4  is from the head strap of the goggles  3  in a direction substantially perpendicular to the direction of contact between the seal portion  4  and the wearer&#39;s face. 
     The seal portion  4  includes inner side walls  48  and outer side walls  49  that extend forwardly, generally in the z-direction, from the sides of the face contact surface. The inner and outer side walls  48 ,  49  effectively provide the two sides of the U-shape discussed above, and connect the face contact surface to the lens cup  31 . The side walls  48 ,  49  are approximately 5 mm high, giving the seal portion  4  a depth of approximately 5 mm. 
     A smooth transition is provided between the contact surface and the side walls, by providing curved corners  481 ,  491  at the interface. A smooth transition improves comfort for the wearer. Preferably, at the medial region  42  of the face contact surface, the radii of the curved corners  461 ,  471  are between 1.2 mm and 3 mm. A smooth transition is particularly important at the medial region  42 , since the contact force between the face contact surface  41  and the wearer&#39;s face is relatively high at this position, and any sharp edges at the interface between the face contact surface  41  and the side walls  48 ,  49  would be very noticeable to the wearer. 
     Referring to  FIGS. 5   b  and  6   b , the face contact surface  41 , and indeed the seal portion  4  as a whole, is considerably curved in the z-direction. The range of deviation of the face contact surface  41  from the best fit plane is approximately 5 mm in the positive z-direction (e.g. as denoted by the arrow  51  in  FIG. 2   b , and approximately 8 mm in the negative z-direction (e.g. as denoted by the arrow  52  in  FIG. 2   b ). This degree of curvature enables the face contact surface  41  to follow substantially the contours of the wearer&#39;s face around the eye socket. 
     The ratio of the spatial extent of the face contact surface in the x-direction, as indicated by arrow  53  in  FIG. 5   a  to the spatial extent of the face contact surface in the y-direction as indicated by arrow  54  in  FIG. 5   a , is approximately 1.4. The distance in the y-direction between the upper and lower regions  44 ,  45  of the face contact surface  41  is approximately 35 mm. This size configuration means that the seal portion  4 , and lens cup  31  do not interfere with the natural movement of the eye and eye lid when worn. 
     A seal portion  6  for goggles according to a second embodiment of the present invention is shown in  FIGS. 7   a ,  7   b ,  8   a ,  8   b  and  9   a  to  9   c.    
     The seal portion  6  is similar to the seal portion  4  of the first embodiment of the present invention, and offers similar advantages. However, there are at least two main differences. Firstly, the seal portion  6  is tubular. Accordingly, a fill substance such as gel (not shown), may be contained entirely within the cavity  69  of the seal portion. (To complete the tubular shape, in addition to the face contact surface  61  and side walls  68 ,  69 , a back panel  611  of the seal portion is provided.) Furthermore, the face contact surface  61  of the seal portion  6  blends into the sidewalls  68 ,  69  of the seal portion in such a manner that there are no corner portions therebetween. Since there are no corner portions, the face contact surface  61  is generally smoother and therefore more comfortable for the wearer. 
     The tubular configuration of the seal portion  6 , and the smooth transition between the face contact surface  61  and the sidewalls  68 ,  69  can be seen most easily in  FIGS. 9   a  to  9   c  which show sectional views along lines A-A, B-B and C-C of  FIG. 7   a , respectively. 
     The seal portion has a relatively flat cross-section at the lateral region  63  of the seal portion  6 , as shown in  FIG. 9   a . The cross section is asymmetric at the medial region of the seal portion  6 , as shown in  FIG. 9   b , whereas the cross section is relatively symmetrical at the upper region  64  of the seal portion  6 , as shown in  FIG. 9   c.    
       FIGS. 10   a  to  10   c  show a seal portion  7  according to a third embodiment of the present invention. The seal portion  7  is integral with a lens cup  8 . The peripheral rear edge of the lens cup  8  provides the face contact surface  71  of the seal portion  7 . The face contact surface  71  is contoured in generally the same manner as the seal portions  4 ,  6  of the first embodiment of the present invention, so that it follows the contours of the wearer&#39;s face around the eye socket. However, the seal portion  8  includes a flange  79 . The flange  79  extends from the face contact surface  71  only at the lateral region  73  of the face contact surface. The flange extends along the central axis of the face contact surface at the lateral region. The flange  79  is resiliently deformable and provides an additional sealing surface to the seal portion  8 , improving further its sealing properties. Having the flange  79  at the lateral region  73  is particularly advantageous, since forces between the face contact surface and the lateral region are fairly low, so it is harder to achieve an effective seal at this position.