Abstract:
A force limiting device for a motor vehicle, which features at least two parts controlled relative to each other with a frequency-based, defined movement, wherein the parts moving relative to each other have mutually engaging gearings and the frequency-controlled movement takes place in such a way that at least one of the parts performs a wave-like advancing motion with respect to another part, in which the gearing is alternately engaged and disengaged, wherein one or a plurality of individual masses are provided, which can be coupled to or decoupled from the part performing the wave-shaped advancing movement thereby changing the force limiting characteristics of the system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to German Patent Application No. 10 2010 026 285.4, filed Jul. 6, 2012 and PCT/EP2011/002775, filed Jun. 7, 2011. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a force limiting device for a motor vehicle belt restraint system. 
         [0003]    Force limiting devices are known in general from various applications in motor vehicles. Steering wheels are known, for example, which collapse in case of a crash due to the impact with the seat occupant, and have a device for energy absorption, by means of which a force acting on the vehicle occupant is limited. Flexible deformation elements are furthermore provided in the entire vehicle body structure, so that energy is absorbed in the event of a crash, so that the force acting on the passenger compartment is limited. 
         [0004]    It is furthermore known from the prior art to provide force limiting elements in the safety belts, so that the force acting on passengers in a crash due to forward displacement is limited by the force limiting device. Two-part belt shafts with a torsion rod arranged between the two parts of the belt shaft have proven useful in the practice. In case of a crash, one part of the belt shaft is locked with respect to the vehicle, while the other part is attached to the safety belt and rotates in the belt extension direction. During the relative rotation of the two parts to each other, the torsion rod arranged between the two parts is plastically deformed about its own axis in an energy consuming manner, so that the force in the safety belt during the forward displacement of the passenger is limited accordingly. The amount of force limiting is determined by the torsion rod and cannot be varied. 
         [0005]    An innovative, frequency-controlled force limiting system is known from patent publication WO 2006/108451 A1 of the applicant. The force limiting system described therein consists of two parts moving with respect to each other, whose movement with respect to each other is controlled by a mass system caused to vibrate or oscillate at a defined frequency. The nullification of the energy takes place in that the parts are alternately decelerated and accelerated, wherein the frequency is essentially independent of the applied force. Different force limiting levels can therefore be attained with this force limiting system as a function of the mass of the moving parts and of the momentum occurring in case of a vehicle impact, wherein the frequency and the path of the forward displacement are approximately constant. 
         [0006]    From WO 2010/037460 A2 is known further development of the force limiting system described therein, in which the force-limited forward displacement of the passenger is made possible in that a part is provided which engages in a gearing of another part and performs a wave-like forward movement in which the gearing is alternately engaged and disengaged. 
         [0007]    The characteristic of the force limiting curve in a system of this kind can be changed by the geometry of the gearing and by the mass of the moving parts. The force limiting characteristic basically can no longer be changed after the part having the gearing has been produced. 
         [0008]    It is an object of the invention to improve a generic force limiting device of the kind described above in such a way that the force limiting characteristic can be varied by the simplest possible means, even after production of the interacting parts. This object is attained according to the invention by means of a force limiting device with the features of this invention. 
         [0009]    In accordance with the basic idea of the present invention, it is proposed to provide one or a plurality of individual masses, which are coupled or can be coupled to the part carrying out the wave-like advancing movement. The mass of the part performing the advancing movement can still be changed subsequently by means of the individual masses, so that the force limiting characteristic can subsequently still be adapted to the individual vehicle. It is accordingly possible to design the force limiting device in such a way that the force limiting characteristic has a specific basic level and/or a basic profile, which can be the force limiting characteristic for the greatest possible number of motor vehicles or motor vehicle types. If this basic level and/or the basic profile is not appropriate for the individual type of motor vehicle, the individual application point in the vehicle, or the individual passenger to be restrained, the force limiting characteristic can be changed by means of the individual masses, wherein in particular the number of individual masses and their mass thereof are available as additional parameters for fine tuning of the force limiting characteristic. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The invention will be described in greater detail below with reference to one exemplary embodiment. The following details can be seen in the figures, wherein: 
           [0011]      FIG. 1  shows a force limiting device according to the invention, in exploded representation; and 
           [0012]      FIG. 2  shows the force limiting device of  FIG. 1  with individual masses coupled to a disk plate with external gearing. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]      FIG. 1  shows a force limiting device according to the invention for a safety belt system of a motor vehicle. The force limiting device can be coupled by means of minor constructive adaptations to the shaft of a belt retractor, the anchor of a belt lock, or also an end stop of a safety belt system. Regardless of the location of attachment to the safety belt system, the force limiting device allows a force-limited extension of the safety belt to reduce the stress acting on the passengers. The use of the force limiting device is furthermore also possible within the structure of the vehicle itself or on another part of the vehicle when a defined force limiting deformation is to be made possible. 
         [0014]    The force limiting device is composed of three parts  1 ,  2  and  3  in this embodiment, wherein the parts  1  and  2  are of a fixed design, and also can be considered to be the housing of the force limiting device. The part  3  is designed as a disk plate with two lateral gearing  12  formed by teeth, of which only the part  1  facing the gearing  12  is shown. The disk plate  13  is furthermore equipped with a radially inwardly directed gearing  7  and an outwardly directed gearing  10 . A drive wheel  5  is provided with a gearing  6 , which is complementary to the gearing  7  and can be connected, for example, in a torque-coupling manner to a belt shaft in order to activate the force limiting device. The fixed parts  1  and  2  are likewise equipped with lateral, axially directed gearings  13  formed by teeth, wherein only the gearing  13  on the part  2  is visible based on the illustration. The gearing  13  and the axially directed (not illustrated) gearing located on the part  1  are shaped in such a way that they engage in the lateral gearing  12  and the gearing, which is not visible, engages in the part  3 , that is, the tooth spacing and the tooth depth of the gearing  12  and  13  and/or of the gearing, which is not illustrated, are selected such that a continuously alternating engagement motion of the gearings is possible. 
         [0015]    The parts  1  and  2  are dimensioned in such a way that the gearing  13  of part  2  and the not illustrated axially directed gearing on the part  1  have a spacing with respect to each other which enables a lateral oscillating movement of the part  3  located between them after the assembly of the force limiting device. As a result of the free play in the axial direction, which is intentionally adjusted as a result of the design, the part  3  is always engaged with the gearing  12  of the part  2  or with the gearing on the part  1 , which is not illustrated. Upon driving the part  3  in circumferential direction by means of the drive wheel  5 , the part  3  carries out the wave-like forward motion caused according to the invention due to engaging in the gearing  12  and in the not illustrated gearing, whereas the part  3  is alternately decelerated and accelerated laterally. The wave-like forward movement of the part  3  is formed by a rotational movement defined by the rotational movement of the drive wheel  5  and a wave-like axial movement directed transversely to the rotational direction of the rotational motion, which is defined by the alternating engagement of the axially directed gearing  13 . The motion sequence corresponds insofar to that of the force limiting device of WO 2010/037460 A2 which is incorporated by reference. 
         [0016]    In accordance with the proposed further development, and as is also evident in  FIG. 2 , a radially outwardly directed gearing  10  formed by teeth is additionally provided transversely with respect to the rotational movement on the part  3 . A plurality of individual masses  4 ,  4   a  and  4   b  having a radial groove  8  facing the part  3  are furthermore provided, in which a gearing  11  formed by teeth is likewise provided, whose geometry is selected in such a way that the gearing  11  can engage in the gearing  10 . 
         [0017]    After an activation of the force limiting device, the individual masses  4 ,  4   a  and  4   b  are taken along by means of the mutually engaged gearing  10  and  11  and laterally by means of the part  3  engaged in the groove  8 , so that the individual masses  4 ,  4   a  and  4   b  in the position coupled to the part  3  likewise carry out the wave-like advancing movement. Due to the selection of the number and mass of the individual masses  4 ,  4   a  and  4   b,  the force limiting characteristic can be individually changed without having to make a design change to the force limiting device per se. A force limiting device is accordingly created, whose force limiting characteristic can be changed as desired with a very small design effort, without the design of the basic elements themselves having to be changed. 
         [0018]    The force limiting device is moreover equipped with a device  14  in the form of a ramp-shaped control contour, which is arranged on the part  2  in a section, which is radially outwardly arranged with respect to the gearing  13 . The control contour runs in a circumferential direction and increases radially outward. The control contour is equipped with an axially protruding lug  14   a,  which features an essentially constant thickness and engages in a groove  9  located to the side of the individual masses  4 ,  4   a  and  4   b.  The lug  14   a  extends laterally from the control contour and has a spiral-shaped profile with a distance to the rotational axis of part  3  that increases in the rotational direction of arrow A. 
         [0019]    With a rotation of part  3  in the direction of arrow A, the individual masses  4 ,  4   a  and  4   b  are additionally guided and carry out a controlled movement by means of which they become disengaged from the part  2  upon reaching a predetermined rotational position. As is evident in  FIG. 2 , one individual mass  4   a  is already in a position in which it no longer engages in the gearing  10  with its gearing  11 ; the individual mass  4   a  is consequently no longer engaged in the part  3 . The individual mass  4   b,  however, is still located in a position in which the gearing  11  and  10  engage with each other, so that the individual mass  4   b  can be considered to be engaged with the part  3 . After an additional rotation of the part  3  with respect to part  2 , the individual masses  4 ,  4   a  and  4   b  are disengaged one after the other by means of a movement of part  3  defined by the control contour and/or the laterally protruding lug  14   a,  so that the entire mass of the part carrying out the advancing movement, which is formed by the sum of the masses of part  3  and of the engaged individual masses  4 ,  4   a  and  4   b,  can be considered as decreasing. A free space  15  arranged radially outward to the moved part  3  is provided to accommodate the disengaged individual masses  4 ,  4   a  and  4   b.  The free space  15  should be dimensioned in such a way that it allows a movement of the individual masses  4 ,  4   a  and  4   a  radially outward by at least the depth of the gearings  10  and  11 , so that the gearings  10  and  11  are no longer engaged in the disengaged position. 
         [0020]    The force limiting characteristic of the force limiting device diminishes as a result of the decreasing total mass, that is, the amount of force limiting decreases if the speed of the part  3  remains constant. An opposite effect can be realized by means of a coupling of the individual masses  4 ,  4   a  and  4   b  during the rotational movement and a consequent increase of the total mass. 
         [0021]    While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.