Abstract:
An impact protection device for a vehicle occupant includes a gas bag, a tension means ( 16 ) and a drawing arrangement ( 22 ). The gas bag has at least one discharge opening ( 12 ). The cross section of the discharge opening ( 12 ) is able to be altered by means of the tension means. The tension means is coupled to the drawing arrangement which is not fastened to the gas bag.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to an impact protection device for a vehicle occupant. 
       BACKGROUND OF THE INVENTION 
       [0002]    An impact protection device with a gas bag which has at least one discharge opening, the cross-section of which is able to be altered by means of a tension means which is coupled to a drawing arrangement is known from EP 0 917 994 A. With this device, a discharge opening can be reduced in size by means of a non-elastic thread which is arranged on the fabric surface of the gas bag and is guided in a loop crosswise around the discharge opening. The outer portions of the thread are guided over expanding regions of the gas bag, and the ends of the thread are fastened on the surface of the gas bag. Thus, as a result of the internal pressure which is produced when a vehicle occupant plunges into the gas bag, a reduction of the cross-section of the discharge opening is achieved which is proportional to the elastic expansion of the gas bag. 
         [0003]    It is an object of the invention to provide an impact protection device with a gas bag, the discharge behaviour of which is individually adjustable by simple means. 
       SUMMARY OF THE INVENTION 
       [0004]    In accordance with the invention, an impact protection device comprises a gas bag, a tension means and a drawing arrangement. The gas bag has at least one discharge opening. The cross section of the discharge opening is being able to be altered by the tension means. The tension means is coupled to the drawing arrangement which is not fastened to the gas bag. The invention is based on the finding that, in particular cases, a reduction of the discharge cross-section is advantageous which is different from a reduction which is dependent on the on the expansion of the gas bag. The impact protection device according to the invention makes possible a controlling of the discharge cross-section which is independent of the expansion. Therefore, after an analysis of the actual case of load, the discharge cross-section can be accordingly adjusted or even varied over time, if necessary with the inclusion of several relevant parameters such as the body weight of the vehicle occupant, severity of impact, type of impact etc. 
         [0005]    In the preferred embodiment of the invention, the tension means has two ends. The first end is connected with the drawing arrangement, and the second end is connected with a fixed component. Alternatively, however, provision may also be made that both ends are connected with a drawing arrangement. In the latter case, the ends of the tension means may either be connected with different drawing arrangements or, with a suitable deflection of the tension means, they may be connected with the same drawing arrangement. 
         [0006]    An electronic control unit which evaluates the relevant parameters of the case of load and causes a corresponding activation of the drawing arrangement is preferably provided for controlling the drawing arrangement. 
         [0007]    According to the preferred embodiment, the drawing device comprises a movable component to which one end of the tension means is coupled. The control unit is able to initiate a movement of the component. To increase the “efficiency” of the drawing arrangement, a gear ratio can be provided, acting between the tension means and the movable component. 
         [0008]    A movement of the component preferably takes place against the resistance of at least one spring element which prestresses the component into an initial position. 
         [0009]    An electromagnet, which can exert an attractive force onto the component, may be provided, for example, for controlling the movement of the component. 
         [0010]    According to a particular aspect of the invention, the impact protection device has a control mechanism coupled to the tension means for altering the cross-section of the discharge opening. The control mechanism is designed so that a drawing on the tension means causes the cross-section to increase in size. This type of construction is suitable for a gas bag which is designed to be relatively hard, i.e. which has a high internal pressure after inflation, in order to provide a sufficient restraining effect for a heavy vehicle occupant, in particular in the case of a heavy impact. In the case of a light vehicle occupant or a less intense impact, the control mechanism can increase the size of the discharge opening in order to adapt the internal pressure of the gas bag accordingly. 
         [0011]    A possible realization of such a control mechanism according to the invention provides a scissor-like element with two rigid arms. The arms are coupled to each other by means of a swivel joint and at least partially surround the discharge opening. Pulling the arms apart brings about an enlargement of the discharge opening. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1   a  discharge opening in a gas bag with an alterable cross-section according to a first embodiment of the invention; 
           [0013]      FIG. 2  a drawing device; and 
           [0014]      FIG. 3  a control mechanism to alter the cross-section of a discharge opening in a gas bag according to a second embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    In  FIG. 1  a portion of a gas bag surface  10  with a discharge opening  12  is shown. A pocket  14  is provided, encircling almost completely on the edge of the discharge opening  12 . The pocket  14  may be formed, for example, by marginal sections of the gas bag material being folded over outwards in the manner of a loop and sewn on the edge on the discharge opening  12 . In this way, a portion of the gas bag fabric, which would otherwise be removed to provide the discharge opening  12 , can be utilized in an efficient and cost-saving manner. 
         [0016]    A tension means  16  in the form of a tear-resistant non-elastic thread or wire is guided in the pocket  14  around the discharge opening  12 , the end sections  16   a ,  16   b  crossing over each other in an outlet region  18  outside the pocket  14 . Inside the pocket  14 , the tension means  16  is fastened to the gas bag at several points which are spaced apart from each other in the peripheral direction. The fastening may take place, for example, by partially sewing on or by sticking fast at points. The crossed-over end sections  16   a ,  16   b  are not fastened to the gas bag and run in opposite directions. Whereas one end  16   c  of the tension means  16  is anchored to a fixed component  20 , e.g. a gas bag module component, a drawing arrangement  22  (not illustrated in  FIG. 1 ) engages on the other end  16   d.    
         [0017]    A possible embodiment of the drawing arrangement  22  is shown in  FIG. 2 . A stationary plate  24  and a movable plate  26  are arranged at a distance from each other which is preset by several compressible springs  28  (initial position). The end  16   d  of the tension means  16  is connected with the movable plate  26  which consists of a magnetizable material. An electromagnet  30  is arranged on the stationary plate  24  so that it can exert an attractive force onto the movable plate  26 . The current supply of the electromagnet  30  takes place by means of an electronic control unit (not illustrated). 
         [0018]    The electronic control unit initially provides for a “base current” to flow through the electromagnet  30 , which is measured such that the attractive force acting on the movable plate  26  corresponds exactly to the restoring force of the springs  28 . In a case of restraint, the attraction can be intensified by increasing the flow of current, and thereby a movement of the plate  26  can be brought about from its initial position against the resistance of the springs  28  towards the stationary plate  24 . Owing to the provision of the base current of the electromagnet  30 , the movement of the plate  26  takes place immediately, because no initial resistance has to be overcome. The movement of the plate  26  corresponds to a drawing at the end  16   d  of the tension means  16 , which leads to a constriction of the discharge opening  12 . Owing to the fastening points which are spaced apart in the peripheral direction, the gas bag fabric can be gathered up in the marginal region of the discharge opening  12 . 
         [0019]    The procedure for constricting the discharge opening can be accelerated by a suitable gear ratio (e.g. in the manner of a reversed pulley) being provided between the tension means  16  and the movable plate  26 . Another possibility is pulling also on the end  16   c  of the tension means  16 . For this, the end  16   c  may be coupled to a further drawing arrangement or, with a suitable deflection of the end section  16   a , to the same drawing arrangement  22 . 
         [0020]    In each case, the electronic control unit provides for a particular tension to be exerted on the tension means  16 , depending on the impact data supplied to the control unit, in order to affect the cross-section of the discharge opening  12  in line with a specific aim. 
         [0021]    A special control mechanism to alter the cross-section of the discharge opening  12  is illustrated in  FIG. 3 . In contrast to the embodiment which was described above, this control mechanism makes possible an enlargement of the cross-section of the discharge opening  12  in line with a specific aim. Here, the pocket  14  is interrupted at least two points in the peripheral direction. Arms  32 ,  34  of a rigid material, which are adapted to the shape of the discharge opening  12 , are inserted into the two pocket parts. The arms  32 ,  34  are part of a control element, constructed in the manner of scissors, which has a swivel joint  36  connecting the arms  32 ,  34 . 
         [0022]    On the side of the discharge opening  12 , the end sections  32   a ,  34   a  of the arms  32 ,  34  each have a hollow profile. An intermediate piece  38  of flexible material can be introduced through the interruption in the pocket  14  into the hollow end sections  32   a ,  34   a  of the arms  32 ,  34 , and can be fastened there. The intermediate piece  38  is either extensible, or a guide is provided in one of the arms  32 ,  34 , within which the intermediate piece  38  can move. 
         [0023]    On the side of the swivel joint  36  facing away from the discharge opening  12 , at least one arm end is connected with a tension means  16  which is, in turn, coupled to a drawing arrangement  22  (not illustrated in  FIG. 3 ). The corresponding end of the other arm may be securely mounted or may be fastened with a further tension means  16  on a fixed component  20 , or may likewise be coupled to a drawing arrangement. A tension spring  40  is provided between the two arms  32 ,  34 , which prestresses the control element into an initial position. In the initial position, the gas bag fabric is gathered around the discharge opening  12 . 
         [0024]    A pulling apart of the arm sections, connected with the tension means, contrary to the prestressing force of the spring  40  causes the arm sections  32   a ,  34   a  to move apart like scissors on the other side of the swivel joint  36 , so that the discharge opening  12  is enlarged. Owing to the gathering of the gas bag fabric around the discharge opening  12 , the enlargement is not impeded by the gas bag fabric.