Abstract:
A method for injection molding of an airbag case comprising a chute channel and a flap, with the chute channel being adapted to receive an airbag. The injection molding is carried out in a mould and comprises the following steps:
       arranging in the mould a net,   manufacturing the flap and the chute channel by injecting plastic matter into the mould, by overmolding plastic matter on the net by manufacturing a continuity of material between the chute channel and the flap, with a portion of the net being isolated from the injected plastic material, in a closed protective space delimited between a wedge mobile and a first matrix of the mould.       
 
     An airbag case in particular manufactures with such a method and dashboard for a vehicle.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to methods for injection molding of an airbag case, to airbag cases and to a dashboard for a vehicle comprising such cases. 
         [0002]    More precisely, this invention relates to a method for injection molding of an airbag case comprising a chute channel, a case and a net. 
       BACKGROUNDS OF THE INVENTION 
       [0003]    Publication DE102010015256 relates to a method for manufacturing an airbag case comprising a chute channel, a case and a net comprising a step of folding the net and a step of maintaining the folds of the net by the intermediary of an assembly element before the manufacturing of the flap and of the chute channel. The folded portion is intended to subsequently form a hinge between the flap and the chute channel. These types of manufacturing methods are already used and provide satisfaction. However, with a concern for reducing the risk of injury to the occupants of the vehicle while still reducing the number of manufacturing steps and the manufacturing time of these safety devices, this invention has objectives to improve this. 
       SUMMARY OF THE INVENTION 
       [0004]    According to a first aspect, this invention relates to a method for injection molding of an airbag case comprising a chute channel delimiting a recess at least partially closed by at least one flap, with the chute channel being adapted to receive an airbag, with the injection molding being carried out in a mould comprising at least first and second mould parts (also called first and second matrices) and a wedge movably mounted with regard to the first matrix, with the method comprising the following steps:
       arranging in the mould a net comprising a first portion, a second portion and a third portion, the third portion being located between the first and the second portion, with the first, third and second portions forming a continuous unit,   manufacturing the flap and the chute channel by injecting plastic material into the mould, by overmolding plastic material respectively on the second portion of the net and on the first portion of the net, with a continuity of material between the chute channel and the flap, with the third portion of the net then being isolated from the injected plastic material, in a closed protective space delimited between the wedge mobile and the first matrix.       
 
         [0007]    A method for the injection molding of an airbag case in few steps is thus obtained, wherein a sealed zone between the flap and the chute channel can be carried out while still providing a portion of the net as “protected”, or in other terms not overmoulded adapted to form a hinge between the flap and the chute channel with a hinge axis mobile between the chute channel and the flap. 
         [0008]    In some embodiments, a person of ordinary skill in the art might also use one or more of the following features taken individually or in combination:
       the wedge is movably mounted in translation with regard to the first matrix between a protective position, wherein the wedge and the matrix close the protective space, and an open position, wherein the wedge and the matrix do not close the protective space. The translation movement of the wedge is easily and quickly carried out for the insertion of the third portion of the net before the step of manufacturing the flap and the chute channel, and for the withdrawal of the third portion of the net after the step of manufacturing the flap and the chute channel;   the first matrix comprises a first surface of the first matrix and the second matrix comprises a first surface of the second matrix, and the wedge comprises a support surface extending along a support direction which, during the step of manufacturing the flap and the chute channel, is substantially in the extension of the first surface of the first matrix and forms with the first surface of the first matrix and the first surface of the second matrix a cavity for the injection of plastic material in order to create the flap. A substantially continuous molding surface of the flap is as such created;   the wedge further comprises a protective surface extending along a protective direction, the protective surface delimiting with a second surface of the first matrix the protective space, and the protective direction and the support direction form between them a non-zero angle between 10° and 80°, more preferably of a magnitude of 45°. In other terms the protective and support surfaces extend along two different directions making it possible to carry out a protective space that is not in the continuity of the support surface, and as such help to ensure the absence of injection of material in the matrix;   the protective surface and the support surface of the wedge have a common edge intended to come facing an intermediate zone extending between the flap and the chute channel during the step of manufacturing the flap and the chute channel. The common edge makes it possible to define a precise zone of separation between the cavity wherein the plastic material is intended to be injected and the protective space, with this zone of separation being in the vicinity of the intermediate zone extending between the flap and the chute channel during the step of manufacturing the flap and the chute channel;   the net comprises a first connecting portion between the first portion and the third portion of the net, and a second connecting portion between the third portion and the second portion of the net, and during the step of manufacturing the flap and the chute channel, the first connecting portion and the second connecting portion are pinched between the common edge and the second surface of the first matrix. In other terms, the “ends” of the third portion of the net directed on the one hand towards the first portion of the net and on the other hand towards the second portion of the net are clamped between the edge of the wedge and the first matrix and close the protective space;   the third portion of the net forms a loop that extends longitudinally in the protective space over a certain length. This arrangement allows for the formation of an extra length of hinge in a reduced space;   the protective surface comprises a projection and the distance between the projection and the common edge is substantially equal to the length of the loop. This arrangement allows sizing the length of the loop;   the chute channel comprises a lateral wall extending along a lateral direction and facing the recess, and a transverse wall extending along a transverse direction, the transverse wall extending substantially in the extension of the flap, with the lateral direction and the transverse direction forming together a non-zero angle, and wherein the net is overmolded in the lateral wall or in the transverse wall. The net is then retained either in the transverse wall of the chute channel (the lateral wall is then not overmoulded) or in the lateral wall (the transverse wall is then not overmoulded) and the risks of detachment of the net and of the chute channel in the case of deployment of the airbag are reduced;   by manufacturing the flap and the chute channel, a continuous or discontinuous line of least resistance and adapted to break facing an intermediate zone extending between the flap and the chute channel is formed. A line is carried out intended to break in case of release of the airbag and ensures a minimum of forces opposing the release of the flap during the deployment of the airbag.       
 
         [0018]    This invention also relates to an airbag case, in particular carried out by a method such as described hereinabove, comprising:
       a chute channel delimiting a recess closed by at least one flap, the chute channel being adapted to receive an airbag,   a net comprising a first portion, a second portion and a third portion, the third portion being located between the first and the second portion, with the first, third and second portions forming a continuous unit,       
 
         [0021]    with the flap and the chute channel being respectively overmoulded by the injection of plastic material on the second portion of the net and on the first portion of the net, with a material continuity between the chute channel and the flap, and the third portion of the net, not overmoulded, extending in the recess. 
         [0022]    Finally, this invention relates to a dashboard for a vehicle comprising an airbag case such as described hereinabove, an inner trim element forming a dashboard body, with the airbag case being fastened onto a surface of the dashboard body, and an airbag arranged in the recess of the chute channel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    Other characteristics and advantages of the invention shall appear when reading the following description of one of its embodiments, provided way of a non-limited example, with regards to the attached drawings. 
           [0024]    In the drawings: 
           [0025]      FIG. 1  is a schematic view in perspective of the passenger compartment of a vehicle provided with a dashboard comprising an airbag case comprising a net, a chute channel and a flap, 
           [0026]      FIG. 2  is a schematic cross-section view of a dashboard comprising an airbag case according to the invention, 
           [0027]      FIGS. 3   a  to  3   d  are schematic cross-section views of successive steps of setting in place in a mould of a net before manufacturing the flap and the chute channel of the airbag case of  FIG. 2  by injecting plastic material into the mould. 
       
    
    
       [0028]    In the various figures, the same references designate identical or similar elements. 
       DETAILED DESCRIPTION 
       [0029]      FIG. 1  schematically shows the passenger compartment of a vehicle  1  provided with a vehicle inner trim part. 
         [0030]    As represented in  FIG. 1 , the inner trim part is a dashboard  10 . However, in alternative embodiments, the inner trim part of the vehicle could be a door panel, a roof trim, a seat or any other type of trim element provided in the passenger compartment of a vehicle. 
         [0031]    Advantageously, the dashboard  10  is a “foamed” board and comprises, such as shown in  FIG. 2 , a dashboard body  11  comprising a layer of rigid support  12 , a layer of foam  14  and a skin  16  covering the layer of foam. The skin  16  and the layer of foam  14  form a covering  18  of the rigid support  12 . 
         [0032]    The skin  16  is one the side intended to be directed towards the passenger compartment of the vehicle. The skin  16  comprises an outer surface, this outer surface can be seen from the passenger compartment and forms the outer surface  20  of the covering  18 . The covering  18  further comprises an inner surface  22 , opposite the outer surface  20 . The inner surface  22  is facing the layer of rigid support  12 . More precisely, the inner surface  22  of the covering  18  is facing an outer surface  24  of the rigid support  12 . 
         [0033]    The rigid support  12  comprises for example an insert made of a rigid plastic material. 
         [0034]    In alternative embodiments, the dashboard could be a dashboard referred to as “injected” comprised of a dashboard body constituting the sole element of the dashboard, or referred to as “thermo-cased” comprising a self-breakable skin covering the dashboard body. 
         [0035]    An airbag case  26  is housed under the dashboard body  11 . More precisely, the airbag case  26  is arranged between the dashboard body and an airbag (not shown). 
         [0036]    Such as shown in  FIG. 2 , the airbag case  26  comprises a chute channel  28 . The chute channel  28  delimits a recess  30 . The recess  30  is adapted to receive an airbag. In a known manner, during the quick inflation of the airbag subsequent to an impact that the vehicle is subjected to, the airbag is deployed through an opening  32  of the recess  30  towards the inside of the passenger compartment. 
         [0037]    The chute channel  28  comprises a lateral wall  34 . The chute channel comprises as represented a second  34 ′, a third and a fourth lateral wall that delimit the recess  30 . The lateral wall  34  comprises an inner surface  36  directed towards the recess  30 . The lateral wall further comprises an outer surface  38  opposite the inner surface  36 . Here, the chute channel comprises a first transverse wall  40 . The chute channel further comprises a second  42 , a third and a fourth transverse wall extending substantially parallel to the covering  18  or to the rigid support  12 . The chute channel  28  is for example made from thermoplastic elastomer. The lateral wall  34  extends according to a lateral direction Xl and the transverse wall  40  creates an angle with the lateral wall  34  and extends according to a transverse direction Xt. 
         [0038]    The safety device  26  (airbag case  26 ) comprises a flap  44 . The flap  44  comes to cover at least partially the opening  32  of the recess  30 . In a preferred embodiment of the invention described hereinafter, the flap  44  comes to fully cover the opening  32  of the recess  30 . This embodiment is particularly suited for so-called “foamed” dashboards. In “normal” use of the vehicle, namely the absence of impacts, the flap  44  closes the opening  32  of the recess  30 . When an impact occurs, the airbag is deployed, comes into contact with the flap  44  and causes the opening of the flap  44 , such as shown as dotted lines in  FIG. 2 . The flap  44  is connected to the chute channel  28  by a hinge connection that allows the pivoting of the flap  44  with regard to the chute channel  28  and limits the projection of the flap  44  in the passenger compartment  1 . For instance, the flap  44  is made of the same material as the chute channel. 
         [0039]    The safety device further comprises a net  46 , more preferably flexible. The net  46  is assembled to the flap  44  and to the chute channel  28  and forms the hinge connection between these two members. More precisely, the net  46  comprises a first portion  48 , a second portion  50  and a third portion  52 . The third portion  52  is located between the first portion  48  and the second portion  50 . The first, third and second portions  48 ,  50 ,  52  form a continuous unit. For example, the first, third and second portions  48 ,  50 ,  52  form a continuous sheet. The net  46  can be either textile, or metal, or any material that is sufficiently resistant. The term “net” designates a flexible material in the form of a sheet, for example woven or even knitted. The net can for example be made of an aromatic polyamide material (also called “aramid”). 
         [0040]    The chute channel  28  and the flap  44  are manufactured by overmolding on the net  46 . 
         [0041]    As described in more detail in what follows, the flap  44  and the chute channel  28  are manufactured, in an injection press, in a mould  54  by overmolding plastic material on the net  46 . The flap  44  is created by overmolding plastic material on the second portion  50  of the net, and the chute channel  28  is manufactured by overmolding plastic material on the first portion  48  of the net. More precisely, the chute channel  28  is carried out by overmolding the transverse wall  40  of the chute channel on the second portion of the net. The lateral wall  34  of the chute channel  28  is not overmoulded on the net  46 . 
         [0042]    For instance, the chute channel  28  and the flap  44  form a single-block part (or are integral). 
         [0043]    The airbag case  26  further comprises a line of least resistance  56 . The line of least resistance  56  is arranged between the flap  44  and the transverse wall  40  of the chute channel  28 . The line of least resistance  56  is continuous. For example the line of least resistance  56  is formed by a notch or a continuous groove. In an alternative embodiment, the line of least resistance is discontinuous. For example the line of least resistance is formed by a plurality of notches that are discontinuous in relation to one another. 
         [0044]    The line of least resistance  56  forms an area intended to be broken, or torn during the deployment of the airbag subsequent to an impact. 
         [0045]    As shown in  FIG. 3   a , the mould  54  comprises a first matrix  58  (or first mould part) and a second matrix  60  (or second mould part). The first and second matrices  58 ,  60  are adapted to cooperate together and define by closing on one another a first cavity  62  for the injecting of plastic material for the creation of the flap  44 . The first and second matrices  58 ,  60  define a second cavity  64  for the injecting of plastic material for the manufacturing of the transverse wall of the chute channel. The first and second matrices  58 ,  60  defining a third cavity  66  for the injecting of plastic material for the manufacturing of the lateral wall  34  of the chute channel  28 . The first, second and third cavities  62 ,  64 ,  66  cooperate together in such a way that the chute channel and the flap form a single-block part. 
         [0046]    The mould  54  further comprises a wedge  68 , such as shown in  FIGS. 2 and 3   a , movably mounted in relation to the first matrix  58 . The wedge  68  and the first matrix  58  delimit a protective space E. Here, the wedge  68  is movably mounted in translation along a wedge direction Xc between a protective position, wherein the wedge  68  and the first matrix  58  close the protective space E, and an open position, wherein the wedge  68  and the first matrix  58  do not close the protective space. 
         [0047]    The wedge  68  comprises a guide surface  70  for its guiding in translation or sliding in a housing  72  provided in the first matrix  58 . 
         [0048]    The wedge  68  further comprises a support surface  74  extending according to a support direction Xa. The support surface  74  is, during the creation of the flap  44  and of the chute channel  28  or, in other terms when the wedge  68  is in its protective position, substantially in the extension of a first surface of the first matrix  76  and forms with the first surface of the first matrix  76  and a first surface of the second matrix  78  the first cavity  62  for the injection of plastic material for the creation of the flap. 
         [0049]    The wedge  68  further comprises a protective surface  80  extending globally according to a protective direction Xp, the protective surface  80  delimiting with a second surface of the first matrix  82 , the protective space E. The protective direction Xp and the support direction Xa form between them a non-zero angle between 10° and 80°, more preferably of a magnitude of 35°. 
         [0050]    The support surface  74  of the wedge  68  extends along the support direction Xa between a first end  84  adjacent to the first surface of the first matrix  76  and a second end  86 . The second end  86  of the support surface  74  constitutes an end of the protective surface  80 . In other terms, the protective surface  80  and the support surface  74  have a common edge  88 . 
         [0051]    The protective surface  80  comprises at a distance d from the common edge  88  along the protective direction Xp a projection  90  directed towards the second surface of the first matrix  82 . The protective space E extends in length between the projection  90  and the common edge  88  and in width between the protective surface  80  and the second surface of the first matrix  82 . 
         [0052]    In protective position of the wedge  68 , the common edge  88  is adapted in order to be substantially located facing an intermediate zone Zi extending between the flap  44  and the chute channel  28 , during the step of manufacturing the flap  44  and the chute channel  28 . The common edge  88  is also adapted to come and pinch the net  46  and isolate from the plastic material injected into the mould the third portion  52  of the net  44  in the protective space E in protective position of the wedge  68 . 
         [0053]    Such as shown in the  FIGS. 2 and 3   a  to  3   d , the third portion  52  of the net  44  forms a loop (or, in other terms is folded) and comprises a first connecting portion  92  between the first portion  48  and the third portion  52  of the net, and a second connecting portion  94  between the third portion  52  and the second portion  50  of the net. The first connecting portion  92  and the second connecting portion  94  form the ends of the third portion  52  of the net. 
         [0054]    The  FIG. 3   a  shows the mould  54  alone in open position with the wedge  68  in protective position. 
         [0055]    During the setting into place of the net  46  into the mould  54  in a preceding step of the manufacturing of the flap and of the chute channel, the wedge  68 , mobile with regard to the first matrix  58 , such as shown in  FIG. 3   b , is first displaced in such a way as to open the protective space E. 
         [0056]    As shown in  FIG. 3   c , then subsequently the first portion of the net  48  is arranged facing surfaces of first and second matrices  58 ,  60  intended to form the second cavity  64 . The second portion  50  of the net is also arranged facing first surfaces of first and second matrices  76 ,  78  intended to form the first cavity  62 . Furthermore, the third portion of the net is arranged which, for instance, forms a loop as described hereinabove, in the protective space E which is open. In an alternative embodiment of the invention, the first portion of the net  48  is arranged in the third cavity  66  in such a way as to extend in the lateral wall  34 , with the second and third portion  50 ,  52  of the net being arranged in a similar manner in the first cavity  62  and the protective space E. 
         [0057]    The last step in the setting in place of the net  46  (or of protecting the third portion of the net from the material to be injected), is the displacement of the wedge  68  from its open position to its protective position in such a way as to close the protective space E by pinching the first connecting portion  92  and the second connecting portion  94  between the common edge  88  and the second surface of the first matrix  82 . 
         [0058]    The airbag case  10  is then subsequently created by closing the mould  54  then by injecting, preferentially during the same step of molding, plastic material into the first, the second and the third cavity  62 ,  64 ,  66  of the mould in such a way as to respectively form the flap  44 , the lateral wall  34  of the chute channel and the transverse wall  40  of the chute channel  28 . 
         [0059]    Finally, the airbag case  10  is unmolded, or removed from its mould  54 . For example the first matrix  58  is made in several portions that are mobile in relation to one another in order to carry out the unmolding. 
         [0060]    The third portion of the net  52 , as shown in  FIG. 2  is not overmoulded and has not been rigidified or made integral with the flap and/or with the chute channel during the manufacturing of the flap and of the chute channel. 
         [0061]    The third portion  52  of the net then forms, as shown in  FIG. 2  a loop between the flap  44  and the chute channel  28  which carries out the function of a hinge. The third portion  52  of the net extends longitudinally substantially 45° from the lateral direction Xl and from the transverse direction Xt. During the deployment of the airbag, the flap  44  tilts in the passenger compartment  1  of the vehicle about an unfastened transverse axis formed by the third portion  52  of the net, which allows for greater freedom of movement, less stress on the flap  44 , less risk of breakage of the flap, and subsequently a decrease in the risk of projection of parts into the passenger compartment of the vehicle. Furthermore, the third portion  52  of the net provides an easy adjusting of the length of the hinge. 
         [0062]    The airbag case  26  is then fastened by the intermediary in particular of the transverse walls  40  of the chute channel  28  onto the rigid support  12 . The fastening is carried out via welding. In an alternative embodiment, the fastening can be carried out by snap-fitting. Advantageously, the airbag case  26  is fastened either onto the outer surface  24  of the rigid support  12 , in particular in the case of a so-called “foamed” dashboard as shown in  FIG. 2 , or onto the inner surface of the rigid support  12  opposite the outer surface  24 , in particular in the case of a dashboard referred to as “injected” or “thermo-lined”. 
         [0063]    The covering  18  then comes to cover the unit formed by the rigid support  12  fastened to the airbag case  26 . The unit formed by the covering  18 , the airbag case  26  and the rigid support  12  is adapted to assemble therein an airbag in the recess  30 . 
         [0064]    The airbag is for example fastened to the airbag case by the intermediary of hooks for example provided to cooperate with an orifice  96  of the lateral wall  34  of the chute channel  28 . 
         [0065]    Such as shown in  FIGS. 1 and 2 , the airbag case  26  further comprises a second flap  98 . The flap  44  and the second flap  98  are arranged to fully close the opening  32 . Such as shown, the flap  44  and the second flap  98  are adjacent in relation to one another and the interface between the two flaps corresponds to a central zone  100  of a line of weakness  102  (shown as a dotted line in  FIG. 1 ). Furthermore, the line of weakness  102  extends on either side of the central zone  100  in such a way as to form a an H substantially delimiting the two flaps  44 ,  98 . 
         [0066]    The second flap  98  is connected to the chute channel by a hinge connection. Such as shown in  FIG. 2 , the hinge connection can consist in a hinge-film formed by a thinning of material forming an interface between the second flap  98  and the chute channel  28  (the second flap  98  and the chute channel  28  being made of a single part (are integral)). 
         [0067]    For encumbrance and safety reasons, the second flap  98  is located on the windscreen side of the vehicle, while the flap  44  is located on the passenger side of the vehicle. 
         [0068]    However, in an alternative embodiment, the second flap  98  is connected to the chute channel by a hinge connection substantially identical to that described hereinbelow for the flap  44 . Preferentially, the second flap  98  is formed with the chute channel  28  during the same step of molding. 
         [0069]    In alternative embodiments of the invention, a single flap  44  covering partially or entirely the opening  32  of the recess  30  can be provided, and for example the line of weakness can have the shape of a “U”.