Patent Publication Number: US-2011057064-A1

Title: Belt retractor

Description:
The invention relates to a belt retractor for a seat belt having the features according to the preamble of claim  1 . 
     A belt retractor of this type is known from German laid-open specification DE 10 2006 026 470 A1. This belt retractor has a belt reel for winding up and unwinding a seat belt, and a lockable locking flange connected to the belt reel. The locking flange and the belt reel are connected by a deformable pin which is pressed into a hole in the locking base and enters an opposite hole in the belt reel. In the event of a relative rotation between the locking base and the belt reel, the deformable pin is bent and, in the process, is pulled out of the hole in the belt reel. The torque required for this increases the belt extension force which can be transmitted by the belt retractor. The level of the belt extension force and the profile thereof can be set via the length of the pin and a suitable choice of material. 
     The invention is based on the object of indicating a belt retractor which is kept structurally simple and can be produced cost-effectively and enables an optimum profile of the belt strap extension force to be set via the belt strap extension length. 
     This object is achieved according to the invention by a belt retractor having the features according to patent claim  1 . Advantageous refinements of the belt retractor according to the invention are indicated in dependent claims. 
     According thereto, it is provided according to the invention that an inner element having a predetermined outer contour is held rotatably in an outer element having a predetermined inner contour, the outer contour or the inner contour having at least one deformable section (R 1 -Rn) by means of which the inner element and the outer element interact and which is deformed in the event of a relative rotation of the two elements, and the inner element being connected to the belt reel and the outer element being connected to the locking base or, conversely, the inner element being connected to the locking base and the outer element being connected to the belt reel. 
     A substantial advantage of the belt retractor according to the invention is that the design of said belt retractor makes it possible for highly individual belt strap extension force profiles to be set: this is because all that needs to be done for this is for the deformable sections, which are provided either on the outer contour or the inner contour of the inner or outer element, to be correspondingly dimensioned. If sections which are thick or are wider, i.e. can be more difficult to deform, are used, higher belt strap extension forces are required in order to unroll the belt strap from the belt reel; if, by contrast, narrower or smaller deformable sections, i.e. sections which are simpler to deform, are used, the belt strap extension force required for unrolling the seat belt from the belt reel will be lower. In other words, the deformable sections therefore permit a specific setting of the belt strap extension force as a function of the belt strap extension length. 
     Another substantial advantage of the belt retractor according to the invention is that it is possible therewith out great effort for, for example, a relatively high restraint force to be achieved by the seat belt at the beginning of a forward displacement of an occupant, and, after unwinding of a predetermined belt strap extension length during the forward displacement of the occupant, for automatic switching over of the restraint force to a lower force level to be achieved. 
     The belt strap extension force can be set in a particularly simple and therefore advantageous manner via the belt strap extension length by the deformable sections being varied in width and/or thickness; in other words, it is therefore considered to be advantageous if there is a plurality of deformable sections differing in width and/or thickness. 
     The deformable sections preferably continuously increase or decrease in width and/or thickness, as seen in the belt unwinding direction of the belt reel, depending on whether a belt strap extraction force which rises with the belt strap extension, i.e. a progressive force profile, or a belt strap extension force which drops with the belt strap extension, i.e. a degressive force profile, is desired. 
     The deformable sections can be formed in a particularly simple and therefore cost-effective manner by compressive ribs, but other designs for the deformable sections are also possible 
     According to a particularly preferred refinement, the inner element or the outer element has at least one thickened portion which deforms the deformable section or the deformable sections in the event of a relative rotation between the inner element and the outer element. The thickened portions may be, for example, cam-shaped and form deformation cams for the deformation of the deformable sections. 
     The inner element or the outer element may also have, for example, a plurality of thickened portions which, for example, are arranged rotationally symmetrically. If, for example, there are three or more thickened portions, said thickened portions can be used for the radial mounting of the inner element within the outer element. 
     The deformable sections are preferably composed of such a material that they are irreversibly plastically deformed in the event of a relative rotation between the inner element and the outer element. 
     In order to simplify deformation of the deformable sections, it is considered to be advantageous if the deformable sections are composed of a softer material than the thickened portions. For example, the deformable sections are composed of aluminum and the thickened portions of zinc. 
     The deformable sections are preferably connected integrally to the inner or the outer element, for example are cast on the inner or the outer, for example annular, element. Casting simplifies the production process and therefore the production costs. 
     The thickened portions are preferably also connected integrally to the inner or the outer element, for example are cast on the inner or the annular element. 
     The outer element can be formed, for example, by an annular element, and the deformable sections can be arranged, for example, on the inner contour of the annular element. 
     According to a particularly preferred refinement, it is provided that the annular element is connected to the belt reel, for example as a single part or by casting, and the inner element is connected to the locking base, for example as a single part or by casting, and the inner element is held coaxially within the annular element of the belt reel. 
    
    
     
       The invention will be explained in more detail below with reference to exemplary embodiments; in the drawings, by way of example: 
         FIG. 1  shows components of a first exemplary embodiment for a belt retractor according to the invention with compressive ribs, wherein three different states of the belt retractor during extension of a belt strap while the locking base is locked are shown in  FIG. 1 , 
         FIG. 2  shows the profile of the belt strap extension force as a function of the respective belt strap extension length for different configurations of the compressive ribs, and 
         FIG. 3  shows components of a second exemplary embodiment for a belt retractor according to the invention, in which three cam-shaped thickened portions are provided for the deformation of deformable sections. 
     
    
    
     In the figures, for the sake of clarity, the same reference numbers are always used for identical or comparable components. 
     An inner element  10  which is mounted rotatably about an axis of rotation D can be seen in  FIG. 1  (left-hand illustration). The inner element  10  has a thickened portion  20  which may be cam-shaped or may form a type of cam. The thickened portion  20  is arranged on the outer contour  30  of the inner element  10  or forms a section of said outer contour  30  of the inner element. 
     Furthermore, an outer element  40  which is of annular configuration and is likewise rotatable about the axis of rotation D and has an inner contour  50  can be seen in  FIG. 1  (left-hand illustration). The inner contour  50  comprises an inner contour region  60  which is equipped with deformable sections in the form of compressive ribs R 1 , R 2 , R 3 , Rn. In addition, the inner contour  50  has a further inner contour region  70  which is free from compressive ribs or does not have any deformable sections in the form of compressive ribs. 
     As can furthermore be seen in  FIG. 1  (left-hand illustration), the inner element  10  and the outer element  40  are arranged coaxially with respect to the axis of rotation D. In this case, at least sections of the inner element  10  engage in the outer element  40  such that the thickened portion  20  of the inner element  10  can interact with the compressive ribs R 1  to Rn of the outer element  40 , in particular if a relative rotation occurs between the inner element  10  and the outer element  40 . 
     The starting point below by way of example is that the inner element  10  forms part of a locking base  100  of a belt retractor (not shown further in detail) and the outer element  40  forms part of a belt reel  110  of said belt retractor. The inner element  10  is preferably connected integrally, for example by casting, to the locking base  100 ; the same applies to the outer element  40 , which is preferably connected integrally, for example by casting, to the belt reel  110 . 
     In the initial position, as shown in the left-hand illustration of  FIG. 1 , the inner element  10  and the outer element  40  are aligned with respect to each other in such a manner that the thickened portion  20  is located within the inner contour region  70  without compressive ribs. 
     If now—for whatever reason, for example due to a person protected by the seat belt of the belt retractor being displaced forward because of inertia—the locking base  100  is locked by said locking base being connected, for example, to a frame of the belt retractor, the belt reel  110  will rotate relative to the locking base  100  if the belt strap extension force is of a sufficient magnitude and exceeds a required minimum force. The minimum force can be predetermined, for example, by any belt force limiting devices present—such as, for example, by one or more torsion bars. This is shown by way of example in the central illustration of  FIG. 1 . 
     It can be seen in the central illustration that the thickened portion  20  of the inner element  10  remains unrotated because the locking base  100  is locked whereas the belt reel together with the outer element  40  thereof is rotated further counter-clockwise along the arrow direction B. Owing to said further rotation, the first compressive rib R 1  is plastically deformed or pressed flat by the thickened portion  20 . The same applies to the compressive ribs R 2  to R 7 , which are likewise deformed. 
     In the central illustration of  FIG. 1 , only the compressive ribs R 8  to Rn have not yet been intercepted by the thickened portion  20  of the inner element  10 , and therefore said compressive ribs are still undeformed. If the outer element  40  or the belt reel  110  is now rotated further relative to the inner element  10  or further relative to the locking base  100 , as is shown by way of example in the right-hand illustration of  FIG. 1 , all of the compressive ribs R 1  to Rn are pressed flat by the thickened portion  20 . Therefore, all of the deformable sections are plastically deformed at the latest after one complete revolution of the belt reel  110  relative to the locked locking base  100  such that said sections can no longer generate any resistance force, or at least any significant resistance force, to a relative rotation between the belt reel  110  and the locking base  100 . 
       FIG. 2  shows by way of example the profile of the belt strap extension force F, to be precise as a function of the respective belt strap extension length L after locking of the locking base  100 . In the illustration according to  FIG. 2 , the starting point by way of example is that the force required for extension of the belt strap after locking of the locking base  100  is composed of a torsion force Ft required for twisting a torsion bar of the belt retractor and of the deformation force Fd required for the deformation of the deformable sections R 1  to Rn. 
     Of course, in addition to a torsion bar or instead of a torsion bar, the belt retractor may also have other force limiting devices which determine the belt strap extension force required for further unrolling of the seat belt from the belt reel. 
     The solid line section  200  in  FIG. 2  shows by way of example the profile of the belt strap extension force F for the situation in which all of the compressive ribs R 1  to Rn are dimensioned identically and the thickened portion  20  requires the same force in each case for deformation of the compressive ribs. 
     Another exemplary embodiment is additionally sketched in  FIG. 2  by means of a dashed line  210 , in which the compressive ribs R 1  to Rn are dimensioned differently, to be precise in such a manner that the force required for deformation or for pressing flat eases off during the extension of the belt strap and a degressive force profile is caused. In order to achieve the digressive profile identified by the reference number  210  in  FIG. 2 , the compressive ribs R 1  to Rn may become, for example, smaller or thinner at an increasing differential angle relative to the thickened portion  20  (as seen from the starting position in the left-hand illustration of  FIG. 1 ) in order to reduce the force required for pressing flat. The profile according to the line  210  can be achieved, for example, if: 
         G ( Ri )&lt; G ( Ri− 1) for 0&lt; i≦n,    
     wherein G(Ri) describes the size or the deformation resistance of the respective compressive rib Ri. In this case, R 1  denotes the first compressive rib which is intercepted and deformed by the thickened portion  20 , and Rn denotes the final compressive rib which is intercepted and deformed by the thickened portion  20 . 
     In addition, a chain-dotted line  220  in  FIG. 2  identifies an exemplary embodiment in which the compressive ribs R 1  to Rn are likewise dimensioned differently, but in a different manner, to be precise such that the force required for rotating the belt reel  110  relative to the locking base  100  increases as the belt strap extension length L increases. A progressive force profile of this type, as indicated by the line  220 , can be caused, for example, by the compressive ribs R 1  to Rn being designed to be continuously thicker and more stable (starting from the first compressive rib R 1  intercepted by the thickened portion  20  to the final compressive rib Rn intercepted by the thickened portion  20 ) in order to make plastic deformation or pressing flat by the thickened portion  20  more difficult as the belt strap extension length increases. The profile according to the line  220  would therefore be achieved specifically if: 
         G ( Ri )&gt; G ( i− 1) for 0 &lt;i≦n,    
     wherein G(Ri) describes the size or deformation resistance of the respective compressive rib Ri. 
     It can also be seen in  FIG. 2  that, after one complete revolution of the belt reel  110  relative to the locking base  100 , the belt strap extension force is no longer determined by the compressive ribs R 1  to Rn but rather a final value denoted by the designation Ft in  FIG. 2  is achieved. The level of the remaining belt strap extension force Ft is therefore not determined by the deformable sections or the compressive ribs but solely or predominantly by other belt force limiting devices, such as, for example, a torsion bar of the belt retractor, if such a torsion bar is present. 
       FIG. 3  shows a further exemplary embodiment in which an inner element  10  is arranged coaxially within an outer element  40  and is rotatable about an axis D within the outer element  40 . 
     In contrast to the exemplary embodiment according to  FIG. 1 , in the exemplary embodiment according to  FIG. 3  the outer contour  30  of the inner element  10  is configured differently. Specifically, the inner element  10  has a total of three thickened portions  20 ,  20 ′ and  20 ″ which can each be designed to be cam-shaped or in the form of cams. 
     The outer element  40  has an inner contour  50  which comprises three inner contour regions  70 ,  70 ′ and  70 ″ without compressive ribs. In addition, there are three inner contour regions  60 ,  60 ′ and  60 ″ which are each provided with deformable sections in the form of compressive ribs R 1  to Rm. 
     In the initial position as shown in the left-hand illustration of  FIG. 3 , the inner element  10  and the outer element  40  are aligned with respect to each other in such a manner that the thickened portions  20 ,  20 ′ and  20 ″ are each located within an associated inner contour region  70 ,  70 ′,  70 ″ without compressive ribs. 
     The inner element  10  is connected, for example, to the locking base of the belt reel. In a corresponding manner, the outer element  40 , for example, forms part of the belt reel of the belt retractor. 
     If the locking base is now locked, a relative rotation between the belt reel and the locking base will occur in the event of a forced extension of the belt strap—for example in the event of a forward displacement of a vehicle occupant. Owing to such a relative rotation, the thickened portions  20 ,  20 ′ and  20 ″ will press the compressive ribs R 1  to Rm flat in the inner contour region  60 ,  60 ′ and  60 ″ in each case associated therewith, thus resulting in a belt strap extension force profile as has been explained by way of example in conjunction with  FIGS. 1 and 2 . 
     A state is illustrated in  FIG. 3  (central illustration) in which the three thickened portions  20 ,  20 ′ and  20 ″ have respectively deformed the first three compressive ribs R 1  to R 3  of the respectively associated inner contour region  60 ,  60 ′ and  60 ″. 
       FIG. 3  (right-hand illustration) shows a state according to which the belt reel  110  has executed a relative rotation of 120° with respect to the locking base and all of the compressive ribs R 1  to Rm of all three inner contour regions  60 ,  60 ′ and  60 ″ have been pressed flat. In this state, the compressive ribs no longer carry out any force-increasing function, and therefore the belt strap extension force required for further extension of the belt strap is determined only by further belt force limiting means, for example torsion bars or the like, if the belt retractor is additionally provided with components of this type. 
     In the exemplary embodiment according to  FIG. 3 , the preferably rotationally symmetrically arranged thickened portions  20 ,  20 ′ and  20 ″ lead to radial guidance of the inner element  10  within the outer element  40  such that additional guidance of the two elements at a different location, for example in a cylindrical region of the belt reel and/or of the locking base, can be omitted. 
     An advantage of the belt retractors described by way of example in conjunction with  FIGS. 1 to 3  is that said belt retractors provide a relatively high restraint force by means of the seat belt at the beginning of a forward displacement of an occupant; after a predetermined belt strap extension length has been unwound during the forward displacement of the occupant, the restraint force is then automatically switched over to a lower force level which is determined, for example, by a torsion bar or by a different force limiting device. In the exemplary embodiment according to  FIG. 1 , the switching over takes place after a belt strap extension length which corresponds to a relative angle of rotation between the locking base and the belt reel of 360°; in the exemplary embodiment according to  FIG. 3 , the switching over takes place after a belt strap extension length which corresponds to a relative angle of rotation between the locking base and the belt reel of 120°. 
     LIST OF DESIGNATIONS 
     
         
           10  Inner element 
           20  Thickened portion 
           20 ′ Thickened portion 
           20 ″ Thickened portion 
           30  Outer contour 
           40  Outer element 
           50  Inner contour 
           60  Inner contour region 
           60 ′ Inner contour region 
           60 ″ Inner contour region 
           70  Inner contour region 
           70 ′ Inner contour region 
           70 ″ Inner contour region 
           100  Locking base 
           110  Belt reel 
           200  Section with constant extension force 
           210  Section with degressive extension force 
           220  Section with progressive extension force 
         D Axis of rotation 
         F Belt strap extension force 
         Fd Deformation force 
         Ft End value 
         L Belt strap extension length 
         P Arrow direction 
         R 1 -Rn Compressive ribs