Abstract:
A seat belt retractor for a safety belt is provided. The retractor includes a seat belt spindle for winding up and unwinding the safety belt and a tensioning drive, which comprises a gas generator, a drive wheel and a supply pipe which connects the gas generator and the drive wheel, a plurality of thrust elements being present in the supply pipe which, after triggering the gas generator, are accelerated and indirectly or directly drive the drive wheel for winding up the safety belt. At least one of the thrust elements is a fiber-reinforced thrust element.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This application is a continuation of International Patent Application Number PCT/DE2011/050015, filed on May 25, 2011, which was published in German as WO 2012/016567. The foregoing international application is incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    Such a seat belt retractor comprising a tensioning drive is known from European patent application EP 1 283 137. The tensioning drive comprises a gas generator, a drive wheel and a connecting device which connects the gas generator and the drive wheel. The connecting device comprises a supply pipe and a multiplicity of thrust elements or thrust members located in the supply pipe, which are accelerated after triggering the gas generator and drive the drive wheel for winding up the safety belt. In the case of the previously known seat belt retractor, the thrust elements consist of metal. 
       SUMMARY 
       [0003]    Proceeding from the described prior art, an object of the invention is to provide a seat belt retractor which exhibits even better operating behavior. 
         [0004]    A seat belt retractor for a safety belt includes a seat belt spindle for winding up and unwinding the safety belt and a tensioning drive. The retractor includes a gas generator, a drive wheel and a supply pipe which connects the gas generator and the drive wheel, a plurality of thrust elements being present in the supply pipe which, after triggering the gas generator, are accelerated and indirectly or directly drive the drive wheel for winding up the safety belt. 
         [0005]    Accordingly, according to a disclosed embodiment of the invention, at least one of the thrust elements (or thrust members) is a fiber-reinforced thrust element. 
         [0006]    A substantial advantage of the seat belt refractor according to an embodiment of the invention can be seen in the fact that, owing to the fiber reinforcement, the thrust elements have greater mechanical stability than thrust elements made from the same material (or a similar material) without fiber reinforcement. The risk of the thrust elements being destroyed during the tensioning operation is therefore reduced and an interference-free tensioning operation is even more reliable. 
         [0007]    The fibers in the fiber-reinforced thrust element particularly preferably have a preferred orientation. By means of a suitable alignment of the preferred orientation, the risk of the thrust elements breaking can be reduced even further. 
         [0008]    The fiber-reinforced thrust element is preferably guided in the supply pipe in such a manner that the alignment of said thrust element and therefore the alignment of the fibers remain the same—with respect to the particular direction of movement—during the movement through the supply pipe. Such an alignment-maintaining guidance can be achieved by a “guiding” shaping of the internal cross section of the supply pipe (for example by means of guide grooves or an angular cross section) or by a fixed or loose chain formation of the thrust elements. The last-mentioned, preferred refinement will be discussed in more detail further below. 
         [0009]    At least half of the fibers of the fiber-reinforced thrust element are particularly preferably at an angle of less than 45 degrees to a mean main fiber direction. The mean main fiber direction therefore forms a preferred orientation of the fibers in the fiber-reinforced thrust element. 
         [0010]    It is considered to be advantageous if the fiber-reinforced thrust element is guided in the supply pipe in such a manner that the angle between the main fiber direction and the particular direction of movement is always smaller than 45 degrees. The effect which can be achieved in the case of this refinement is that the stability-increasing effect of the fibers is maintained even if the thrust elements are guided through curved sections of the supply pipe. 
         [0011]    The angle between the main fiber direction and the particular direction of movement is preferably always smaller than 10 degrees (for example 0 degrees±5 degrees). The main fiber direction particularly preferably corresponds to the particular direction of movement. 
         [0012]    The thrust elements may be, for example, in the shape of a drum and/or may be round, elliptical or angular in cross section. However, it is considered to be particularly advantageous if the fiber-reinforced thrust elements have an axis of symmetry. The angle between the axis of symmetry and the main fiber direction is preferably smaller than 10 degrees (for example 0 degrees±5 degrees), and the axis of symmetry and the main fiber direction particularly preferably rest one on the other. The symmetry of the thrust element may be, for example, rotational symmetry. 
         [0013]    The fiber-reinforced thrust element is particularly preferably guided in the supply pipe in such a manner that the angle between the axis of symmetry and the particular direction of movement during the movement through the supply pipe is smaller than 45 degrees and particularly preferably smaller than 10 degrees (for example 0 degrees±5 degrees). 
         [0014]    If the thrust elements are produced within the scope of a casting or injection molding process, it is considered to be advantageous if the injection is undertaken at an angle of between 0 degrees and 30 degrees—with respect to the longitudinal axis of the thrust element or with respect to the subsequent direction of movement of the thrust elements. In the case of such an injection angle, an automatic alignment of the longitudinal direction of the fibers of the cast material in the longitudinal direction of the thrust elements and therefore along the subsequent direction of movement of the thrust elements can be achieved in a particularly advantageous manner. 
         [0015]    At least two consecutive thrust elements in the supply pipe are preferably partially plugged one into the other and form an (at least two-membered) thrust element chain. The thrust elements which are partially plugged one into the other are preferably plugged in loosely or releasably and form a releasable thrust element chain. 
         [0016]    For the loose chain formation, at least one thrust element in the supply pipe preferably has at least one plug-in section which is plugged into a recess in an adjacent thrust element in the supply pipe. The plug-in section and the recess are preferably dimensioned in such a manner that the thrust elements which are plugged one into another can pivot relative to one another. This makes it possible to bend the forming thrust element chain and to push the latter through curved regions in the supply pipe. The effect which can be achieved by the combination of plug-in section and recess is that the alignment of the thrust elements relative to the particular direction of movement is maintained during the tensioning operation. 
         [0017]    It is also considered to be advantageous if two or more thrust elements are connected fixedly to one another forming a twin group (pair or thrust elements), a triple group or a multi-membered thrust element chain. 
         [0018]    In order to form a nonreleasable thrust element chain, the thrust elements are, for example, connected to one another, specifically preferably by means of one or more strand-shaped links. 
         [0019]    According to a first particularly preferred variant embodiment, the thrust elements of the thrust element chain are connected to one another by webs. The webs are preferably already formed during the production of the thrust elements. The thrust element chain is preferably produced within the scope of an injection molding process, in which the thrust elements of the thrust element chain and the webs are cast together. The injection point or the injection points of the injection molding material containing the fibers or the injection point or the injection points of the injection molding material into the injection mold are preferably at least also located at the or in the region of the end of the thrust element chain. The injection is particularly preferably carried out at an angle of between 0 degrees and 30 degrees—with respect to the longitudinal axis of the thrust element chain or with respect to the subsequent direction of movement of the thrust elements. In the event of an injection point in the region of the chain end and/or by the selection of a corresponding injection angle, the injection molding material can be pressed in a particularly simple manner through the web regions of the injection mold, thus resulting in a particularly advantageous manner in automatic alignment of the longitudinal direction of the fibers of the injection molding material in the longitudinal direction of the chain and therefore along the subsequent direction of movement of the thrust elements because the fibers are automatically aligned as the latter pass the web regions. 
         [0020]    According to a second particularly preferred variant embodiment, the thrust elements are connected to one another by a flexible, strand-shaped link, in particular a cable or a wire. The strand-shaped link is preferably guided through at least two thrust elements. 
         [0021]    The strand-shaped link is particularly preferably embedded in the fiber-reinforced material of at least two thrust elements, in particular cast with the fiber-reinforced material of at least two thrust elements. It is also considered to be advantageous in this case if the injection is undertaken at an angle of between 0 degrees and 30 degrees—with respect to the longitudinal axis of the thrust element chain and with respect to the subsequent direction of movement of the thrust elements. In the event of such an injection angle, an automatic alignment of the longitudinal direction of the fibers of the injection molding material in the longitudinal direction of the chain and therefore along the subsequent direction of movement of the thrust elements can be achieved in a particularly advantageous manner. 
         [0022]    In a particularly advantageous refinement, it is provided that at least one of the thrust elements consists of a fiber-reinforced, for example glass-fiber-reinforced, plastic or at least also contains such a material. 
         [0023]    A substantial advantage of this particularly preferred refinement can be seen in the fact that said thrust element may have a lower weight than previously known seat belt retractors. This is because fiber-reinforced plastic is less dense than metal. When fiber-reinforced plastic is used, the weight reduction of the thrust element assembly may be up to 80%, compared with a thrust element assembly consisting of metal. 
         [0024]    A further substantial advantage of this particularly preferred refinement can be seen in the fact that said thrust element also reliably functions even in the event of an external action of heat. This is because, in contrast to metal thrust elements, fiber-reinforced thrust elements have the advantageous property of less frequently jamming in the supply pipe even in the event of external heating than is the case for thrust elements consisting of metal. Jamming of the thrust elements may be based, for example, on deformation, melting and/or on an increase in volume of the thrust elements in the event of external heating; such a temperature-induced jamming of the thrust elements is less severe in the case of thrust elements made from fiber-reinforced plastic than in the case of metal thrust elements. 
         [0025]    A third substantial advantage of this particularly preferred refinement resides in the lower production costs in comparison to conventional seat belt retractors, since fiber-reinforced plastic is significantly more cost-effective than metal. 
         [0026]    A fourth substantial advantage of this particularly preferred refinement can be seen in the fact that the drive system according to an embodiment of the invention is more rapid than the corresponding drive systems in previously known seat belt retractors; this is because the inertia of thrust elements consisting of fiber-reinforced plastic is lower because of the lower density than the inertia of metal thrust elements. 
         [0027]    A fifth substantial advantage of this particularly preferred refinement consists in that the noise produced during the operation is lower than in the case of seat belt retractors consisting of metal. 
         [0028]    A sixth substantial advantage of this particularly preferred refinement can be seen in the fact that the receptacle in which the thrust elements are collected after triggering of the drive is subjected to a less severe load than is the case with thrust elements made of metal. This is because—as already mentioned—fiber-reinforced plastic has a lower density and therefore the mass which has to be collected by the collecting body is smaller than in the case of thrust elements made of metal. 
         [0029]    All of the thrust elements preferably consist of fiber-reinforced plastic. 
         [0030]    The fibers of the fiber-reinforced plastic are preferably (exclusively or at least also) glass fibers, but use may also be made of fibers of a different material, such as, for example, of ceramic or carbon (carbon fibers). The thrust element material can therefore be, for example, glass-fiber-reinforced plastic. 
         [0031]    For the described use particularly suitable plastics materials are polyamide and polyphthalamide; accordingly, it is considered to be advantageous if the fiber-reinforced plastic at least also contains polyamide and/or polyphthalamide. 
         [0032]    If polyamide is used, use is preferably made of a heat-stabilized, partially crystalline polyamide. 
         [0033]    The fiber-reinforced plastic is particularly preferably reinforced with long fibers (for example long glass fibers). The fibers of the fiber-reinforced plastic preferably have a length of at least 0.2 mm, particularly preferably a length of at least 0.5 mm. 
         [0034]    The fiber content of the fiber-reinforced plastic is preferably at least 20%, particularly preferably at least 50%. 
         [0035]    The density of the fiber-reinforced plastic is preferably maximum 2.0 g/cm 3 , particularly preferably maximum 1.6 g/cm 3 . 
         [0036]    It is also considered to be advantageous if the fiber-reinforced plastic is impact-resistant modified. 
         [0037]    The strain at break of the fiber-reinforced plastic is preferably at maximum 5%, particularly preferably at maximum 3% or at maximum 2%. 
         [0038]    The stress at break of the fiber-reinforced plastic is preferably at least 200 N/mm 2 . A stress at break range of between 200 and 300 N/mm 2  is considered to be advantageous. 
         [0039]    The fiber-reinforced plastic can be formed, for example, by GRIVORY GVL-6H material or may at least also contain such a material. 
         [0040]    Furthermore, it is considered to be advantageous if between the drive wheel and the seat belt spindle an inertia coupling is arranged which comprises coupling elements which, during an acceleration of the drive wheel, pivot outward and are directly or indirectly coupled to the seat belt spindle. An advantage of this refinement can be seen in the fact that, as a result of the pivotability of the coupling elements, after the end of the tensioning process it is possible to disengage said coupling elements again, whereby the tensioning drive may once more be separated from the seat belt spindle. 
         [0041]    Preferably, contact surfaces of the coupling elements are formed such that they remain engaged in the tensioning rotational direction under load, and may be disengaged in the load-free state and/or in the direction of extension of the seat belt. 
         [0042]    The coupling elements may, for example, be formed by coupling claws, coupling catches, coupling drums or coupling wedges. 
         [0043]    The seat belt spindle preferably comprises a tubular inner wall into which the contact surfaces of the coupling elements are directly forced when pivoted outward. In this refinement, the number of parts, and thus also the weight of the seat belt retractor, are at an optimum. The contact surfaces of the coupling elements are preferably grooved. 
         [0044]    According to a particularly preferred refinement of the seat belt retractor, it is provided that the grooved contact surfaces of the coupling elements are serrated and have alternate steep and flat edges. 
         [0045]    Preferably, the steep and flat edges are formed such that the force is transmitted to the seat belt spindle at least substantially by the flat edges. 
         [0046]    Preferably, the inertia coupling comprises a coupling disk which is connected to the drive wheel and is formed by an inner ring, an outer ring and at least one resilient connecting element, the coupling elements and a guide disk of the inertia coupling being inserted into the coupling disk such that, with an acceleration of the drive wheel by the gas generator, the inner ring and the guide disk are rotated relative to the outer ring due to the resilient action of the resilient connecting element(s) such that stops of the outer ring pivot the coupling elements outward. 
         [0047]    Preferably, the resilient connecting elements are configured such that, when the tensioning force of the tensioning drive drops, the relative rotation between the inner ring and the outer ring is canceled such that the coupling elements are pivoted by further stops of the outer ring back into their initial position before the tensioning process. 
         [0048]    In order to ensure the coupling of the seat belt spindle and the coupling elements in any angular position without jerky movements, it is considered to be advantageous if the tubular inner wall is smooth before the initial contact with the coupling elements. 
         [0049]    The invention also relates to a method for producing a seat belt retractor. According to an embodiment of the invention, fiber-reinforced thrust elements or a thrust element chain consisting of fiber-reinforced thrust elements are/is formed by casting or injection molding. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0050]    The invention is described in more detail hereinafter with reference to exemplary embodiments; in this connection and by way of example: 
           [0051]      FIGS. 1-14  show a first exemplary embodiment of a seat belt retractor according to the invention in various views, 
           [0052]      FIGS. 15-16  show a second exemplary embodiment of a seat belt retractor according to the invention, 
           [0053]      FIG. 17  shows an exemplary embodiment for a pair of thrust elements comprising two thrust elements which are connected to each other and consist of fiber-reinforced plastic, 
           [0054]      FIGS. 18-20  show an exemplary embodiment in which the thrust elements form a loose thrust element chain, 
           [0055]      FIGS. 21-23  show an exemplary embodiment in which the thrust elements form a fixedly connected thrust element chain, and 
           [0056]      FIG. 24  shows an exemplary embodiment with a thrust element chain in which the thrust elements are connected by connecting webs. 
       
    
    
     DETAILED DESCRIPTION 
       [0057]    In the figures, for the sake of clarity, the same reference numerals are used for identical or comparable components. 
         [0058]    In  FIG. 1 , an exemplary embodiment of a seat belt retractor  10  is seen in a schematic exploded view. The seat belt retractor  10  comprises, inter alia, a seat belt spindle  20 , a tensioning drive  30  and an inertia coupling  35  connecting the tensioning drive  30  and the seat belt spindle  20 . 
         [0059]    The tensioning drive  30  comprises a pyrotechnical gas generator  40 , for example in the form of a micro gas generator, a drive wheel  50 , a curved supply pipe  60  connecting the gas generator  40  and the drive wheel  50 , and also a plurality of inertia elements or thrust elements  70 . 
         [0060]    The thrust elements  70  are, for example, spherical. All of the thrust elements preferably consist of a glass-fiber-reinforced plastic. All of the thrust elements are preferably identical to one another. 
         [0061]    The drive wheel  50  is rotatably held between a retaining cap  51  and a retaining plate  52  and has holder shells  100  in which the thrust elements  70  engage in order to drive the drive wheel. The thrust elements  70  are, to this end, engaged tangentially in the drive wheel  50  and run tangentially past said drive wheel, engaging in the holder shells  100 , in order to pass subsequently into a receptacle  110  arranged downstream. 
         [0062]    The holder shells  100  of the drive wheel  50  are preferably formed such that the thrust elements  70 , when engaged in the drive wheel  50 , are always spaced apart from one another and are not in contact with one another; this is, for example, shown in more detail in  FIGS. 2 and 3 . The force transmission preferably takes place in this case by a positive connection or at least also by a positive connection. The number of thrust elements  70  is preferably greater than the number of holder shells  100  of the drive wheel  50 , and therefore the drive wheel  50  is able to rotate completely about its own axis more than simply once. 
         [0063]    Preferably, the sealing of the supply pipe  60  takes place solely by means of the thrust elements, for example the thrust elements  70   a ,  70   b  and  70   c , which—as viewed from the gas generator  40 —form the first thrust elements  70  in the supply pipe  60 . Sealing of the supply pipe is otherwise not required, but may nevertheless be additionally provided. 
         [0064]    Preferably, the supply pipe  60  in the engagement region  120 , in which the thrust elements  70  are engaged in the drive wheel  50 , has a resilient tubular wall portion  120 , by means of which the engagement behavior is optimized and jamming of the thrust elements in the drive wheel  50  is avoided. The resilient tubular wall portion  120  may, for example, have a flat end portion  121  with a T-shaped fastening element  122 . 
         [0065]    The first thrust element, i.e. the thrust element next to the drive wheel, is preferably prefixed in the delivery state of the tensioning drive  30  in a holder shell  100  of the drive wheel  50 , by the drive wheel  50  itself being prefixed by means of a breakable fixing, for example in the form of a shear pin;  FIG. 4  shows this in more detail. 
         [0066]    As may be seen from  FIG. 5 , the supply pipe  60  is preferably provided with two apertures, namely a pressure relief aperture  130  in the region of the gas generator  40  and a control aperture  140  in the central region of the supply pipe  60  between the gas generator  40  and the drive wheel  50 . 
         [0067]    The control aperture  140  may, for example, be formed by an opening in the supply pipe  60 ; the pressure in the supply pipe  60  is reduced by means of this opening when the last thrust element—i.e. the thrust element located closest to the gas generator  40 —passes this opening. The tensioning force of the tensioning drive  30  is reduced as a result of the drop in pressure, and therefore, for example, the tensioning process may be stopped due to the counteracting seat belt extraction force. The opening is, however, preferably of sufficiently small size for the tensioning process not to be terminated solely by the drop in pressure and for all thrust elements  70  to be fired into the receptacle  110 , in spite of the drop in pressure, whilst allowing a sufficiently high seat belt extraction force. 
         [0068]    The pressure relief aperture  130  preferably prevents excess pressure of the tensioning drive  30 . 
         [0069]    The tensioning drive  30  is shown again in  FIG. 6  from above in a different view;  FIG. 7  shows the seat belt retractor  10  in the mounted state. It may be seen from the two  FIGS. 6 and 7  that the gas generator  40  and the drive wheel  50  are fastened to different portions  150  and  160  of a C-shaped carrier  170  of the seat belt retractor  10  and are spatially separated from one another by the seat belt spindle  20 . 
         [0070]    In  FIG. 8 , the coupling of the drive wheel  50  to the inertia coupling  35  and the coupling thereof to the seat belt spindle  20  are shown again in more detail in a section. 
         [0071]      FIGS. 9 ,  10  and  11  show the components according to  FIG. 1 , again enlarged and in detail. 
         [0072]    In  FIGS. 12 ,  13  and  14 , the construction of the inertia coupling  35  is shown by way of example. A coupling disk  200  may be seen, connected to the drive wheel  50  and driven thereby, and which is formed by an inner ring  201 , an outer ring  202  and resilient connecting elements  203 . Three coupling elements  210 ,  220  and  230  which may be pivoted outward and also a guide disk  240  are inserted into the coupling disk  200 . In order to prevent the coupling elements  210 ,  220  and  230  from falling out of the guide disk  240 , a cover plate  241 , for example, may be present which by means of latching elements  242  and  243 , for example, is latched to the coupling disk  200 .  FIG. 13  shows the relative position between the guide disk  240  and the outer ring  202  in the initial state. 
         [0073]    The inner ring  201  and the guide disk  240  are connected to the drive wheel fixedly in terms of rotation. If the drive wheel  50  is accelerated in the rotational direction P by the torque M of the tensioning drive  30 , the inner ring  201  is rotated relative to the outer ring  202  due to the resilient action of the resilient connecting elements  230  as a result of inertia such that stops  245  of the outer ring  202  pivot the coupling elements  220 ,  230  and  240  outward (see  FIG. 14 ) and said coupling elements with their grooved contact surfaces  250  are driven into the tubular inner wall  260  of the seat belt spindle  20  which is preferably smooth, i.e. formed without grooves or the like, whereby the coupling elements are connected to the seat belt spindle  20  and the coupling is engaged. The force of the coupling elements is denoted by the force vector {right arrow over (F)}k. The force transmission by the flat edges is denoted by the force vector {right arrow over (F)}f. 
         [0074]    If the tensioning force of the tensioning drive  30  is reduced, for example because the gas generator  40  is used up, and may no longer provide sufficient drive pressure, or after completing the tensioning process the seat belt spindle is rotated in the direction of extension of the seat belt, the relative rotation between the inner ring  201  and the outer ring  202  is again cancelled due to the resilient action of the resilient connecting elements  203 , and therefore the coupling elements  210 ,  220  and  230  are pivoted back by further stops  246  of the outer ring  202  into their initial position (see  FIG. 13 ) before the tensioning process, and are once more separated from the seat belt spindle  20 , and therefore the drive wheel  50  may not be rotated in the direction of extension of the seat belt. 
         [0075]    The driving of the coupling elements into the inner wall  260  and the pivoting back of the coupling elements for the purpose of disengagement is made much simpler by the serrated shape of the contact surfaces  250 , which have alternate steep and flat edges. As may be seen from  FIG. 14 , the serrated shape is selected such that the force transmission relative to the inner wall  260  is carried out by the flat edges. The flat edges, during the coupled state, are at a shallower angle relative to the inner wall  260  than the steep edges. It may be seen that the force vector of the flat edges {right arrow over (F)}f relative to the force vector {right arrow over (F)}k of the coupling elements is rotated by the alignment of the flat edges, and namely by an angle of between preferably 0 and 45 degrees and in the direction of the torque M and/or in the tensioning rotational direction P. 
         [0076]    Preferably, a seat belt force limiting mechanism is not provided in the force transmission path between the tensioning drive  30  and the seat belt spindle  20 , i.e. neither between the drive wheel  50  and the inertia coupling  35  nor between the inertia coupling  35  and the seat belt spindle  20 . The seat belt force is preferably limited only in the direction of extension of the seat belt, and namely by a torsion bar, not shown further, which with one end is rigidly connected to the seat belt spindle and with its other end to a locking mechanism of the seat belt retractor  10 . 
         [0077]    The seat belt retractor is preferably fixedly fastened to the vehicle frame (fixed to the frame). Each tensioning drive, for example for lap belt tensioning and/or shoulder belt tensioning, preferably has its own gas generator. 
         [0078]    In  FIGS. 15 and 16  a further exemplary embodiment of a seat belt retractor  10  is shown. In this exemplary embodiment, a backstop device in the form of a pivotable spring element  300  is present, which may be passed in only one direction by the thrust elements running past the drive wheel  50 , namely in the direction of the receptacle  110 . The spring element  300  thus prevents, for example, the last thrust element  70   n  from being able to be moved back again toward the drive wheel  50  after completing the tensioning process. 
         [0079]      FIG. 17  illustrates an exemplary embodiment of a pair of thrust elements  400  consisting of two thrust elements  70  which are connected to each other and each consist of fiber-reinforced plastic. The connecting region  410  between the two thrust elements  70  preferably also consists of fiber-reinforced plastic. 
         [0080]      FIG. 18  shows an exemplary embodiment in which the thrust elements  70  are plugged loosely one in another. For this purpose, the thrust elements  70  each have a plug-in section  500  in the form of a plug-in lug which is plugged into a recess  505  in the form of a blind hole in the respectively adjacent thrust element  70 . By the thrust elements  70  being plugged one into another, a loose thrust element chain  510  is formed, the longitudinal direction of which corresponds to the direction of movement B of the thrust elements  70  in the supply pipe of the seat belt retractor. 
         [0081]    By means of the formation of the thrust element chain  510 , guidance of the thrust elements  70  in the supply pipe is achieved, specifically in such a manner that the alignment of the thrust elements in the thrust element chain  510  and the alignment of the thrust elements in the supply pipe remain the same—with respect to the particular direction of movement B during the movement through the supply pipe. 
         [0082]      FIG. 19  shows one of the thrust elements  70  according to  FIG. 18  in cross section. It may be seen that the thrust element  70  consists of a fibrous material. The fibers  515  in the fiber-reinforced thrust element  70  are not oriented randomly but rather have a preferred orientation. The preferred orientation arises by the fact that at least half of the fibers  515  are at an angle of less than 45 degrees to a mean fiber direction—called the main fiber direction here—which is denoted by the reference symbol V in  FIG. 19 . The preferred orientation of the fibers therefore defines the main fiber direction V. 
         [0083]    It may also be seen in  FIG. 19  that the fiber-reinforced thrust element  70  is rotationally symmetrical and has an axis of symmetry S. The axis of symmetry S is preferably identical to the main fiber direction V; at least, the angle between the axis of symmetry S and the main fiber direction V should preferably be smaller than 10 degrees. By means of this fiber alignment, a particularly high degree of stability of the thrust elements  70  in the direction of movement B is achieved in an advantageous manner, and therefore the thrust elements can withstand the high mechanical loadings precisely in the acceleration phase. 
         [0084]    In the exemplary embodiment according to  FIGS. 18 and 19 , the thrust elements  70  are loosely connected to one another by being plugged one in another. As an alternative, groups of two or more thrust elements can also be fixedly connected to one another and can form, for example, twin or triple groups. Such twin and triple groups are shown by way of example in  FIG. 20  and are denoted by the reference numerals  530  and  535 . 
         [0085]      FIG. 21  shows an exemplary embodiment in which the thrust elements  70  are connected to one another by a flexible, strand-shaped link  550 . A mechanically flexible thrust element chain  555  is formed by the strand-shaped link  550 . 
         [0086]    The flexible, strand-shaped link  550  may be, for example, a cable or a wire. The flexible, strand-shaped link  550  preferably consists of plastic and/or metal, for example steel. 
         [0087]    The thrust element chain  555  according to  FIG. 21  is preferably produced within the scope of a casting process, in particular injection molding process, in which the strand-shaped link  550  is cast into the fibrous material of the thrust elements. 
         [0088]      FIG. 22  shows one of the thrust elements  70  of the thrust element chain  555  according to  FIG. 21  in cross section. It may be seen that the strand-shaped link  550  is embedded, preferably cast, into the fibrous material of the thrust elements. 
         [0089]    In addition, it may be seen that the main fiber direction V of the fibers  515  is identical to the longitudinal direction of the axis of symmetry S, the longitudinal direction of the strand-shaped link  550  or the longitudinal direction of the thrust element chain  555  and to the direction of movement B. Such directional identity is not absolutely necessary, but it is considered to be advantageous if the angle between the main fiber direction V and the longitudinal direction of the strand-shaped link  550  or the longitudinal direction of the thrust element chain  555  and the direction of movement B is at least smaller than 10 degrees. 
         [0090]      FIG. 23  shows the thrust element chain  555  according to  FIG. 21  in a view from the side. It may also be seen here that the strand-shaped link  550  is embedded in the fibrous material of the thrust elements and extends through a plurality of thrust elements. 
         [0091]      FIG. 24  shows an exemplary embodiment of a thrust element chain  600  in which the thrust elements  70  of the thrust element chain are connected to one another by webs (connecting webs)  610 . The webs  610  are preferably already formed during the injection molding of the thrust elements  70  by the thrust element chain  600  being injected or cast in a single piece including the webs  610 . The injection point A (or the injection points) of the injection molding material  620  containing the fibers is preferably at least also located at or in the region of the end of the thrust element chain  600 . 
         [0092]    A preferred injection angle α for the injection direction of the injection molding material  620  may be seen in  FIG. 24 . The injection angle α is preferably between 0 degrees and 30 degrees with respect to the longitudinal axis of the thrust element chain  600  and with respect to the subsequent direction of movement of the thrust elements  70 . The angle shown in  FIG. 24  relates by way of example to the center point  630  of the thrust element  70  at which the injection is taking place. 
         [0093]    Preferably, the injection is carried out at or in the region of the end of the thrust element chain  600 ; this has the advantage that the injection molding material is forced through the web regions of the injection mold, thus resulting in a particularly advantageous manner in an alignment of the longitudinal direction of the fibers of the injection molding material in the longitudinal direction of the chain and therefore along the subsequent direction of movement of the thrust elements. 
         [0094]    The webs  610  between the thrust elements  70  may be elastic (by means of an appropriate choice of material) in order to enable bending of the thrust element chain  600  in regions of curvature of the supply pipe. As an alternative, the webs  610  may also be rigid or of such stiffness that they prevent bending of the thrust element chain  600 ; in this case, the webs  610  will break when they are introduced under pressure into regions of curvature of the supply pipe during the assembly of the seat belt retractor, or are pressed through the supply pipe during the subsequent tensioning operation. 
         [0095]    In order to permit casting or injection molding of the thrust chain and subsequent breaking of the webs, a web diameter of between 0.1 mm and 10 mm is considered to be advantageous. The maximum web diameter is produced from the requirement that the webs may break when passing through curvatures in the supply pipe; the minimum web diameter is dependent on the viscosity of the thrust element material to be cast or to be injected. The viscosity of the thrust element material is determined by the basic material, i.e., for example, by the type of plastic, and the concentration of the fibers: the greater the concentration of fibers, the more viscous is the thrust element material to be cast or injected, and the size of the web diameter should be selected, with regard to the casting or injection molding process, in accordance with the degree of viscosity of the thrust element material in order to enable the thrust element material to be able to pass the web regions in the casting mold during the casting or injection molding. If the thrust element material is too viscous and the web region is too small, the casting/injection molding is made more difficult or even impossible. In the case of many materials, in particular in the case of plastics, such as polyamides, and/or a fiber concentration of between 40% and 70% (60%±5% are considered preferable), a web diameter within the range of between 1 mm and 3 mm is particularly advantageous: such a diameter permits casting/injection molding, and the webs are nevertheless thin enough to be able to break as they pass through curvatures in the supply pipe. 
         [0096]    The thrust element chain  600  can be introduced into the supply pipe, for example, by a filling pipe which is placed onto the supply pipe and permits the thrust element chain  600  to be introduced under a sufficiently high pressure such that a breaking of the webs  610  may optionally occur. 
         [0097]    The priority application, German Patent Application No. DE 10 2010 033 184.8; filed on Aug. 3, 2010 is incorporated by reference herein. 
       LIST OF DESIGNATIONS 
       [0000]    
       
           10  Seat belt retractor 
           20  Seat belt spindle 
           30  Tensioning drive 
           35  Inertia coupling 
           40  Gas generator 
           50  Drive wheel 
           51  Retaining cap 
           52  Retaining plate 
           60  Supply pipe 
           70  Thrust element 
           100  Holder shells 
           110  Receptacle 
           120  Tubular wall portion 
           121  End portion 
           122  T-shaped fastening element 
           130  Pressure relief aperture 
           140  Control aperture 
           150  Portion 
           160  Portion 
           170  U-shaped carrier 
           200  Coupling disk 
           201  Inner ring 
           202  Outer ring 
           203  Resilient connecting elements 
           210  Coupling claw 
           220  Coupling claw 
           230  Coupling claw 
           240  Guide disk 
           241  Cover plate 
           242  Latching element 
           243  Latching element 
           245  Stops 
           246  Further stops 
           250  Contact surface 
           260  Inner wall 
           300  Spring element 
           400  Pair of thrust elements 
           410  Connecting region 
           500  Plug-in section 
           505  Recess 
           510  Loose thrust element chain 
           515  Fiber 
           530  Twin group 
           535  Triple group 
           550  Strand-shaped link 
           555  Mechanically flexible thrust element chain 
           600  Thrust element chain 
           610  Web 
           620  Injection molding material 
           630  Center point 
         A Injection point 
         α Injection angle 
         B Direction of movement 
         {right arrow over (F)}k Force vector 
         {right arrow over (F)}f Force vector 
         M Torque 
         P Tensioning rotational direction 
         V Main fiber direction 
         S Axis of symmetry