Abstract:
A self-locking belt retractor has a belt reeling shaft having a belt connected thereto. A locking device, activatable in a vehicle sensitive and/or belt-sensitive manner for preventing belt removal from the belt reeling shaft is provided. The locking device has a locking member and a profiled head connected to the belt reeling shaft. The belt reeling shaft is locked when the locking member engages the profiled head. At least two force-limiting elements are arranged in parallel or in series to one another, wherein one of the force-limiting elements is a torsion bar allowing a limited belt removal when the locking device locks the belt reeling shaft. A switching device for selectively engaging at least one of the force-limiting elements is provided to thereby connect the belt reeling shaft and the profiled head. The switching device is switched between the force-limiting elements and the belt reeling shaft for adjusting the energy absorption of the belt retractor and adapting the belt retractor to pre-adjustable incidents of loading.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a self-locking belt retractor with a locking device that is activated in a vehicle-sensitive and/or belt-sensitive manner, whereby the belt retractor has as a force-limiting device a torsion bar that allows, when the locking member is engaged a limited belt removal and is connected, on the one hand, to the belt reeling shaft and, on the other hand, by a profiled head to the locking member of the belt retractor. A device for adjusting the energy absorption of the torsion bar and adjusting the torsion bar to preselected incidents of loading is switched in the force-transmitting path between the torsion bar and the belt reeling shaft. 
     A self-locking belt retractor with the aforementioned features is known from DE 27 27470 A1. Inasmuch as the known belt retractor has a torsion bar as a force-limiting device, for an individual adjustment of the force level of the belt force limitation to the respective parameters set by the passenger, a continuos change of the clamping length of the torsion bar as a function of the weight of the passenger seated in the vehicle seat and/or of the allowed forward movement path is realized. For this purpose, a sliding sleeve connected to the belt reeling shaft and adjustable over the length of the torsion bar is provided which can be moved by an actuating device and, depending on its position, determines the torsion force and thus the free torsion length of the torsion available for force limitation. 
     In theory, the clamping length does not affect the force level for the belt force limitation, instead only the energy absorption capacity of the torsion bar is changed. Practical experiments in this context have shown that the effect of the clamping length of the torsion bar onto the force level is minimal and is not sufficient for practical applications. The invention has therefore the object to improve a belt retractor of the aforementioned features such that a change of the force level is possible over a wide adjustment range and furthermore also possible directly at the beginning or during an accident as a function of the loading conditions occurring in individual situations. 
     SUMMARY OF THE INVENTION 
     The invention is based on the principal idea that at least two force-limiting elements, arranged in parallel or in series relative to one another and controllable by a switching device that adjusts the energy absorption are provided, whereby one of the force-limiting elements is embodied by the torsion bar. 
     The inventive other force-limiting element, according to one embodiment of the invention, is embodied as a torsion sleeve surrounding the torsion bar whereby the torsion bar and/or torsion sleeve are connectable by a coupling element to the belt reeling shaft. 
     For this purpose, in a first embodiment it may be provided that the belt reeling shaft radially engages the end of the torsion bar and the torsion sleeve, respectively, and that at the belt reeling shaft a respective coupling pawl for the torsion bar as well as the torsion sleeve is arranged as a coupling element. Alternatively, it may be provided that the coupling element is embodied as a follower disc positioned at the end of the belt reeling shaft opposite the profiled head in positive locking, axially slidable connection with the belt reeling shaft. In its coupling position the follower disc couples the torsion bar and the torsion sleeve with one another by follower pins penetrating correlated abutting flanges of the torsion bar and the torsion sleeve. 
     In a second embodiment of the invention the adjustment of the force level is achieved in that as the other force-limiting element at least one resistance body is connected to the end of the belt reeling shaft opposite the profiled head. It revolves in a housing filled with a suitable material and is position-adjustable relative to the torsion bar. 
     In an alternative embodiment of the invention it may be provided that as the other force-limiting element the end of the belt reeling shaft opposite the profiled head is provided with a paddle wheel circulating in a housing filled with a suitable material whereby in the housing a friction plate is arranged so as to be axially moveable for adjustment of the material density. 
     Finally, in another embodiment of the invention, it is suggested that as a device for controlling the energy absorption capacity of the force-limiting device the torsion bar has at least two portions over its length separated by a connecting piece and having different cross-sections and that the portions of the torsion bar can be connected respectively to the belt reeling shaft by a coupling element between the belt reeling shaft and the respective connecting piece. In this context, the respective torsion bar can be embodied of two but also of three serially and formed-lockingly arranged or connected torsion bars. 
     With respect to the embodiment, respectively, arrangement of the coupling element, according to one embodiment of the invention it may be provided that either the end of the torsion bar is connected to the belt reeling shaft and the connecting piece separating the portions of the torsion bar are connectable by a controllable coupling pawl, supported at the belt reeling shaft, to the belt reeling shaft, or that alternatively at the end of the torsion bar a further connecting piece is arranged and as a coupling element a slide is provided that is fixedly coupled with respect to rotation to the belt reeling shaft, but axially moveably arranged thereat, and form-lockingly engages the connecting pieces. In this manner, it is possible to respectively couple the portions of different cross-sections of the torsion bar directly to the belt reeling shaft. 
     In more detail, according to one embodiment of the invention, it may be provided that at the connecting piece a sleeve surrounding the torsion bar may engage in a positive-locking manuever and the coupling pawl may be designed for fixation at the sleeve, whereby in an expedient manner the coupling pawl can be actuated by a pyrotechnical ignition pill arranged within the cross-section of the belt reeling shaft. 
     In another embodiment of the invention a multi-step adjustment of the torsion bar is provided instead of the two-step adjustment of the force limitation, and in this context it is suggested that, for adjusting a three-step energy absorption of the torsion bar, three portions separated by two connecting pieces are provided with different stepped cross-sections and each connecting piece has coordinated therewith a separate sleeve with coordinated coupling pawl. 
     Inasmuch as the connection between torsion bar and belt reeling shaft in individual cases is achieved by a sliding sleeve, it may be provided that as a coupling element a sliding sleeve is provided that is fixedly coupled with respect to rotation to the belt reeling shaft, but axially moveably arranged thereat, and engages the connecting pieces in a positive-locking manner. 
     In such an embodiment of the invention it may also be provided that the sliding sleeve is displaceable by a pyrotechnical ignition pill arranged within the cross-section of the belt reeling shaft. In this embodiment the gases released by the ignition pill will enter directly into the area of the sliding sleeve and will load it with respect to an axial movement. 
     As an alternative drive for the movement of the sliding sleeve it may be provided that for actuation of the sliding sleeve a pressure chamber is provided at the corresponding end face of the belt reeling shaft. A sliding disc is moveably arranged therein and the sliding disc is connected by a pawl engaging the disc and an attached pusher rod to the sliding sleeve and that the pressure chamber has an externally arranged ignition pill for releasing a pressure gas. 
     In this embodiment a three-step adjustment of the energy absorption is also provided since, for adjusting one of the three steps of the energy absorption level, the torsion bar has three portions separated by two connecting pieces with different stepped cross-section and the sliding sleeve is movable between the two connecting pieces and can be coupled by the movement selectively to each connecting piece. Two ignition pills acting respectively on the two sides of the sliding disk are connected to the pressure chamber. 
     As a further control of the force limitation it may be provided that for switching off the torsion bar the belt reeling shaft is lockable to a pressure ring rotatably supported the housing of the belt reeling shaft, whereby the pressure ring can be secured in a full load position by a pawl activated by a pyrotechnical ignition pill. 
     It may be expedient, after completion of the force limitation with rotation of the torsion bar, to prevent a further rotation of the belt reeling shaft in the removal direction in order to prevent overload of the torsion bar, it may be provided that the rotatably supported pressure ring has coordinated therewith a further stop pawl which is pivotable by the pressure ring that rotates with switched-on torsion bar into a stop position in which the stop pawl, upon continuing rotation of the pressure ring, provides a fixed stop for the pressure ring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawing embodiments of the invention are disclosed which will be described in the following. It is shown in: 
     FIG. 1 a self-locking belt retractor with force limiting device in a schematic sectional representation; 
     FIG. 1 a  the coupling area of the device for adjusting the force level according to FIG. 1 in an enlarged representation; 
     FIG. 2 the object of FIG. 1 in a further embodiment; 
     FIG. 3 the belt retractor with force limiting device in a further embodiment according to the representation of FIG. 1; 
     FIG. 3 a  the device for adjusting the force level in an enlarged representation; 
     FIG. 4 the object of FIG. 3 in another embodiment; 
     FIG. 5 a belt retractor with force limiting device in a representation according to FIG. 1 in a further embodiment with a multi-step torsion bar and switching device that is pawl-actuated; 
     FIG. 6 the object of FIG. 5 in a further embodiment with a three-step adjustable force level; 
     FIG. 7 a belt retractor with force limiting device in the representation according to FIG. 5 in a further embodiment with a sliding sleeve as a switching device; 
     FIG. 8 the object of FIG. 7 in an embodiment with a three-step force level; 
     FIG. 9 the object of FIG. 8 with an alternative drive for the sliding sleeve as well as with a full load locking and abutment for the rotation of the belt reeling shaft; 
     FIG. 10 the force limiting device according to FIG. 9 in an exploded view of its individual parts; 
     FIG. 11 the full load locking with stop according to FIG. 9 in an end view with switched-on full load locking; 
     FIG. 12 the object of FIG. 11 after activation of the stop pawl by rotation of the belt reeling shaft. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The belt retractor respectively represented in the individual drawing figures is comprised of a U-shaped housing  10  having a belt reeling shaft  13  supported in the respective legs  11  of the U-shape, respectively, in the penetrations  12  arranged therein. At the locking end of the belt reeling shaft  13  a profiled head  14  is arranged at the shaft end face and revolves in the leg  11  of the U-shaped housing  10  whereby at the profiled head  14  a locking member (not represented) is supported that is radially deflectable under the effect of a non-represented control device. Due to the activation in the case of a deceleration, the locking member can be moved into a correlated toothing arranged in the penetration  12 . 
     The profiled head  14  and the belt reeling shaft  13  are connected to one another by a torsion bar  15  acting as a force-limiting device. One end of the torsion bar  15  is preferably positive-lockingly connected to the profiled head  14  and the other end of the torsion bar  15  extending within the belt reeling shaft  13  is connected to the belt reeling shaft  13 . For this purpose, the end opposite the profiled head  14  of the belt reeling shaft  13  engages the projecting end in the form of a radially projecting flange  17 , whereby the flange  17  is provided with an outer toothing  18  as can be seen in FIG. 1 a.  At the end of the belt reeling shaft  13  a first coupling pawl  16  is supported which, upon engagement of the outer toothing  18 , couples the torsion bar  15  and the belt reeling shaft  13  to one another. 
     As an additional force limiting element a torsion sleeve  19  is provided that surrounds the torsion bar  15  and is also connected to the profiled head  14 . The torsion sleeve has a radial flange  20  adjacent to the flange  17  of the torsion bar  15  which is also provided with an outer toothing  18  whereby a second coupling pawl  21  is arranged at the belt reeling shaft  13 . The coupling pawls  16 ,  21  can be selectively activated by a control device  23  which in the shown embodiment is a solenoid. As a function of the determined parameters such as seat position, height and weight of the passenger, the vehicle velocity or the inflation behavior of the air bags, it is possible to switch on only the torsion bar  15  or only the torsion sleeve  19  or torsion bar  15  and torsion sleeve  19  together by activating the respectively correlated coupling pawl(s)  16 ,  21  into the force transmitting path between the profiled head  14  supporting the locking member and the belt reeling shaft  13  so that in this manner a different force level can be selected. 
     In the embodiment represented in FIG. 2 the radially active coupling between the torsion bar  15 , respectively, the torsion sleeve  19  and the belt reeling shaft  13  is replaced by an axially movable and positive-lockingly connectable follower disk  24  connected to the belt reeling shaft  13  which axially penetrates the correlated flanges  17 ,  20  of torsion bar  15 , respectively, torsion sleeve  19  with follower pins  25 . For axial movement of the follower disk  24  an angled lever as control lever  26  is provided whose movement results in a movement of the follower disk  24 . Depending on the position of the follower disk  24  only the torsion bar  15  or, in a parallel switching position, also the torsion sleeve  19  is connected to the belt reeling shaft  13 . 
     According to the embodiment represented in FIGS. 3,  3   a,  the side of the housing  10  of the belt retractor opposite the profiled head  14  is connected to a housing  27  filled with a gel filling  28  whereby the end of the belt reeling shaft  13  extending into the housing  27  supports two oppositely arranged resistance bodies  29  that are radially adjustable by a control device  30  in their position relative to the torsion bar  15 . The control of the force limitation is provided by the displacement resistance which results from the resistance bodies  29  being forced through the gel filing  28  during the rotational movement between the profiled head  14  and the belt reeling shaft  13 . An adjustment of the force level is to be provided by the radial position of the resistance bodies  29  for which purpose the control device  30  is comprised of a coupling to the housing  27  and a gear wheel  30  and toothed rods  31  coupled thereto as a support of the resistance bodies  29 . This braking device must be turned off in normal operation and must be switched on in an accident situation. 
     In the corresponding embodiment represented in FIG. 4, the end of the belt reeling shaft  13  with its projection  32  extends into the housing  27  provided with a gel filling  28  whereby on the projection  32  a paddle wheel  33  is provided via which the force level can be adjusted. The control of the force level is realized individually by an axially movable pressure plate  34  in the housing  27  whereby its position in the housing determines the density of the gel filling  28 . 
     In the embodiment represented in FIG. 5 it is suggested that the torsion bar along its length has at least two portions  36  separated by a connecting piece  35  and provided with different cross-sections. While the end of the torsion bar is directly connected to the end of the belt reeling shaft  13 , the connecting piece  35  separating the portions  36  of different cross-sections is engaged by a sleeve  38  extending to the end of the belt reeling shaft  13  whereby at its end similar to the embodiment of FIGS. 1,  1   a  a radially projecting flange  20  with outer toothing  18  is arranged whereby at the end of the belt reeling shaft  13  a controllable coupling pawl  21  is arranged. In this embodiment, only the first portion  36  of the torsion bar  15  having the greater cross-section can be engaged by contact of the coupling pawl  21  with the belt reeling shaft  13  whereby the second portion  36  of the torsion bar  15  is bridged by the sleeve  38 . When the coupling pawl  21  does not engage the sleeve  38 , the belt reeling shaft  13  will load the torsion bar  15  over its entire length so that the thinner area  36  of the torsion bar  13  is twisted and a lower force level is adjusted. 
     In the embodiment represented in FIG. 6 the torsion bar  15  has three consecutive portions  36  with stepped cross-sections whereby the portions  36  are separated by two connecting pieces  35 . Each connecting piece  35  has correlated therewith a sleeve  40 ,  42  and each sleeve  40 ,  42  is lockable by a corresponding pawl  41 ,  43  to the belt reeling shaft  13  surrounding the sleeve  40 ,  42 . The pawls  41 ,  43  are locked in their initial position between the sleeve  40 ,  42  and the belt reeling shaft  13 . When an accident occurs, they are released by an ignition pill  39  respectively arranged and coordinated in a cross-section of the belt reeling shaft. This has the advantage that the transition from one locking position into a release position is safely realized which is easier than realizing a locking action during an accident. 
     When during an accident, for example, both pawls  41 ,  43  remain locked, both connecting pieces  35  are then coupled by the corresponding sleeves  40 ,  42  to the belt reeling shaft  13  and the torsion bar  15  with its portion facing the left side, respectively, the profiled head is loaded which corresponds to a high force level. When during the accident a release of the pawl  41  occurs, the portion of the torsion bar  15  between the two connecting pieces  35  having a reduced cross-sectional area is thus loaded so that the force level is lowered. When subsequently also the pawl  33  is released, the belt reeling shaft, because of its connection to the torsion bar, only loads the portion of the torsion bar  15  at the right external portion with minimal cross-section which corresponds to a minimal force level. 
     In the represented embodiment a full load locking is additionally possible by the full load pawl  44  between the profiled head  14  and the belt reeling shaft  13 , i.e., a switching off the torsion bar  15  is realized because upon locking of the full load pawl  44  a relative rotation of the belt reeling shaft  13  to the profiled head  14  supporting the locking member is not possible. When the profiled head  14  is locked by the locking member arranged thereat, the torsion bar  15  is thus turned off. 
     In the embodiment represented in FIG. 7, a further connecting piece  35  is arranged at the end of the torsion bar  15  whereby a slide  37  is provided that engages form-lockingly the two connecting pieces  35 . The slide is fixedly connected to the belt reeling shaft  13 . The slide  37  is axially movable by a control lever according to the embodiment of FIG.  2 . It allows activation, depending on its position, only of the first portion  36  with comparatively large cross-sectional area of the torsion bar  15  or of the entire torsion bar  15  in the position displaced to the right, including the further smaller cross-sectional area  36  by connecting it to the belt reeling shaft  13 . 
     Inasmuch as in the embodiments an adjustment of the force level is provided with the control  23 , the control lever  36 , the control device  30  or the friction plate  34 , these control parts can be, for example, mechanically activated by a cable pull or electrically by an electric motor or by activation of a solenoid. 
     In FIG. 8 a variant of the embodiment represented in FIG. 7 is represented in which the torsion bar  15  is also designed to have a three-step force level as disclosed already in connection with the embodiment of FIG. 6 in detail. A sliding sleeve  47  is arranged such between the two connecting pieces  35  of the torsion bar  15  that the sliding sleeve can be moved in both directions along the torsion bar  15  so that it can be selectively coupled due to its connection to the belt reeling shaft to one or the other connecting piece  35  at the belt reeling shaft  13 . For activation of the sliding sleeve  47  ignition pills  45 ,  46  are provided within the cross-section of the belt reeling shaft  13  whereby their ignition provides for movement of the sliding sleeve  47 . Otherwise, the adjustment of the force level is carried out in the same manner as disclosed in FIG.  6 . In the embodiment represented in FIG. 8 a full load pawl  44  for locking the profiled head  14  at the belt reeling shaft  13  is also provided. 
     The embodiment represented in FIG. 9 differs from the embodiment represented in FIG. 8 in that the drive for the sliding sleeve  47  is arranged external to the belt reeling shaft  13 . Accordingly, there are no problems with respect to the arrangement of the required chambers for receiving the ignition pills within the shaft and there is also no danger of a pressure increase that is too high within the shaft. Also, no sliding contacts for the control of the ignition pills are required. At the end face of the belt retractor housing  10  a pressure chamber  48  is arranged in which in the shown embodiment with a three-step adjustment of the force level a sliding disk  49  is arranged in a central position which can be moved within the pressure chamber  48  in two directions. By a pawl  51  the sliding disk is connected to a sliding rod  50  that is itself connected to the sliding sleeve  47 . The two ignition pills  45 ,  46  for movement of the sliding sleeve  47  are connected to the pressure chamber  48  whereby one ignition pill is provided on each side of the sliding disk  49  in order to effect the movement of the sliding disk  49  in different directions and to thus also move the sliding sleeve  47  in different directions. 
     As a further improvement with respect to the embodiments of FIGS. 6 and 8, in the embodiment of FIG. 9 the full load locking is realized between the belt reeling shaft  13  and the housing  10  so that the connection between the profiled head  14  and the belt reeling shaft  13  is relieved. At the outer side of the corresponding leg  11  of the housing  10  a pressure ring  61  with an inner toothing (FIGS. 11,  12 ) is rotatably supported such that the belt reeling shaft  13  provided with a correlated outer toothing is supported during an accident by engagement of the toothings and by the resulting blocking of the belt reeling shaft  13  due to the locking member supported at the profiled head. For switching off the torsion bar by full load locking the pressure ring  61  is lockable by a pawl  62  as is shown in FIG.  11 . For this purpose, the pressure ring  61  at its outer circumference has a cam  64  which in the rotational direction of the belt reeling shaft  13  upon removal of belt is blocked by the engaged pawl  62 . The pawl  62  can be pivoted by a correlated ignition pill  63  pyrotechnically out of the movement path of the cam  64  so that for switching on the torsion bar the ignition pill  63  is activated and the pawl  62  is pivoted into its release position for the pressure ring  61 . In the shown embodiment a stop function is also realized for force limitation at the end of the allowable rotational movement of the belt reeling shaft, wherein at the housing additionally a stop pawl  65  is supported such that in the pivoted state it blocks the cam  64  of the pressure ring  61 . For activating it, the stop pawl  65  in its release position projects with a projection  66  into the movement path of the cam  64  of the pressure ring  61  so that the cam  64 , after rotation of the belt reeling shaft  13 , respectively, of the pressure ring  61  coupled thereto, pivots via the stop at the projection  66  the stop pawl  65  into its stop position so that this stop position after a further, i.e., second revolution of the belt reeling shaft  13  will be activated and locks the belt reeling shaft  13 . This stop thus is activated earlier than breakage of the torsion bar  15  of the force limitation would occur. 
     With the activated pawl  62  according to FIG. 11, the torsion bar is switched off because upon blocking of the profiled head the outer toothing of the belt reeling shaft  13  will engage the toothing of the pressure ring  61  and is thereby supported at the non-rotatable pressure ring  61  secured by the pawl  62  so that the force limitation is switched off by a further rotation of the belt reeling shaft provided by the torsion bar. 
     The features of the inventive device disclosed in the above description, the claims, the abstract and the drawing can be important individually or in any suitable combination with one another for realizing the invention in its various embodiments. 
     The specification incorporates by reference the entire disclosure of German priority documents 196 25 541.4 of Jun. 26, 1996, and 197 20 473.2 of May 15, 1997, as well as of International Application PCT/EP97/03284 of Jun. 23, 1998. 
     The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.