[ 0019 ] fig1 represents a gas bag module which has a gas bag 3 , a gas generator 5 and a module housing 7 with a module cover 9 . the gas generator 5 is surrounded by a pot - or bell - shaped diffuser 10 , which has been put over the gas generator 5 from above and is attached to the module , to be more precise at the module housing 7 . the gas bag has a gas bag wall including several regions or portions , for instance a front wall 11 which faces the occupant in the inflated condition and restrains the same , as the occupant impacts onto it . the gas bag wall defines the outer contour of the inflated gas bag . moreover , a rear wall 12 is provided . in the middle of the gas bag , i . e . in the center , a depression 17 extends from the front wall 11 towards the gas generator 5 . the depression 17 is formed in that a portion of the outer gas bag wall , subsequently referred to as center portion 16 , is prevented from moving out of the module in the case of restraint . as a result , a ring - shaped chamber 18 to be inflated and to be filled with gas is obtained . the depression 17 , however , is not to be inflated . the module cover 9 has a middle portion 19 which adjoins the center portion 16 and is permanently attached to the diffuser 10 . for the attachment of this middle portion 19 , a reinforcement sheet is provided inside the middle portion , from which reinforcement sheet threaded bolts protrude , which extend through the center portion 16 and the diffuser 10 , so as to be screwed with nuts from below . as a result , the center portion 16 is positively attached to the diffuser and also frictionally clamped between the middle portion 19 and the diffuser 10 . in the folded condition , the gas bag 3 is accommodated in an annular space 20 between the diffuser 10 and an outer wall of the module housing 7 . moreover , the cover 9 has a ring - shaped cap 21 composed of segments , which cap covers a ring - shaped outlet opening 22 when the gas generator 5 is not yet activated . in the interior of the chamber 18 , there are provided two limiting straps 23 , 24 disposed opposite each other with respect to the depression 17 , which limiting straps extend from the front wall 11 as far as to the center portion 16 and are sewn to the front wall 11 and the center portion 16 . the limiting straps 23 , 24 are shorter than the length s of the part of the gas bag wall 25 bridged by them , so that in the inflated condition as shown in fig1 the limiting straps 23 , 24 are tensioned and determine the depth t of the depression and of the gas bag . due to the limiting straps 23 , 24 extending alongside the depression 17 , the part of the gas bag wall 25 defining the depression 17 can bulge towards the depression 17 to such an extent that portions 26 close to the transition 27 between the front wall 11 and the depression 17 contact each other , so that the depression is substantially completely closed from the outside . as a result , a substantially completely closed restraining surface is provided for the occupant . fig2 to 4 in particular refer to the attachment of the limiting strap to the gas bag wall . in the embodiment as shown in fig2 the gas bag consists of four ring - shaped fabric layers . a first fabric layer 30 above all forms the rear wall 12 . a second fabric layer 32 in particular forms the front wall 11 . the fabric layer 32 has a centric opening , which is formed in that an h - shaped slot is cut into the fabric layer 32 . there are obtained two substantially square fabric tabs 34 , which in the inflated condition project towards the gas generator , and to each of which a limiting strap 23 , 24 is sewn . to the edge of the opening in the fabric layer 32 there is likewise sewn a ring - shaped fabric layer 36 , so that the opening is closed to the outside . the fabric layer 36 forms the upper part of the depression 17 . the outer edge of a fabric layer 38 , which is likewise ring - shaped , is in turn sewn to the inner edge of the fabric layer 36 . the fabric layer 38 extends as far as to below the middle portion 19 and includes the center portion 16 . the lower ends of the limiting straps 23 , 24 are sewn to the fabric layer 38 in the region of the center portion 16 . in the inflated condition , the opening in the fabric layer 32 is closed in that the fabric layer 36 bulges radially to the inside and in part also to the top , so that portions 26 of the fabric layer 36 rest against each other and close the depression 17 , as is shown in fig5 . in fig5 the limiting straps 23 , 24 are also represented in broken lines . the embodiments in accordance with fig3 and 4 substantially correspond to the embodiment shown in fig2 so that only the differences will be discussed . as shown in fig3 the fabric layer 32 has an oval , rectangular or slotted opening to whose edge the fabric layer 36 is sewn . the limiting straps 23 , 24 are then attached to the fabric layer 36 at a distance from the surrounding seam 51 . in accordance with this embodiment , there is obtained a relatively small depression 53 in the region of the front wall which for better clarity is represented exaggeratedly deep in fig3 . the limiting straps 23 , 24 extend as far as to below the middle portion 19 and completely overlap each other in this region and are sewn to the fabric layer 38 also below the middle portion . in the embodiment as shown in fig3 the limiting straps 23 , 24 are thus attached to the gas bag wall defining the depression 17 , but still directly at the transition 27 from the front wall 11 to the depression 17 . in the embodiment as shown in fig4 not only the fabric portions 32 and 36 are sewn to each other by the surrounding seam 51 , but at the same time the limiting straps 23 , 24 are sewn to the gas bag wall . in this embodiment , however , the limiting straps 23 , 24 are integrally connected with each other below the middle portion 19 , i . e . a long strip of fabric is provided , both ends of which form the limiting straps 23 , 24 . in this embodiment , the depression 17 can be closed almost over the entire depth t , since the gas bag wall can bulge to the inside to such an extent that portions of the gas bag wall rest against each other over a large surface . the ring - shaped front wall 11 is thereby completely closed . the particularity of this feature is that contrary to fig3 no depression 53 is formed , but in the inflated condition of the gas bag the portions 57 of the fabric layer 36 rather lie outside a plane e which is defined by the points of attachment 51 of the limiting straps 23 , 24 to the front wall 11 . in the region of the portions 57 the gas bag thus bulges to the outside in the direction towards the occupant , opposite to the depression 17 , or it lies in the plane e . the illustrated form can also be extended such that , as shown in broken lines , a surrounding bead 59 can be formed . with a view to the front wall 11 , the gas bag presents itself to the occupant as a closed impact surface , and only in the middle folds 60 can be seen , with portions 26 of the gas bag wall , which defines the depression , resting against each other . [ 0031 ] fig6 a to 6 g represent various blanks of the fabric layer 32 , which forms the front wall 11 , as well as the position of the limiting straps 23 , 24 . moreover , in the inflated condition the openings will be much smaller than in the blanks illustrated . [ 0032 ] fig6 a represents an h - shaped opening 71 , from which the depression extends to the inside . in the embodiment as shown in fig6 b , a t - shaped opening 71 is provided . [ 0034 ] fig6 c shows a c - shaped opening 71 , which can also be closed by only one limiting strap 23 , where appropriate . in the embodiment as shown in fig6 d , a square opening 71 is provided , and in the embodiment as shown in fig6 e an oval opening 71 . fig6 f shows a triangular opening 71 and three limiting straps 23 , 24 , 75 , which are arranged at an angle of 120 ° with respect to each other .