Abstract:
A belt retractor for a vehicle safety belt comprises a belt spool ( 12 ) rotatably mounted in a frame ( 10 ) and a coupling disc ( 32 ) rotatably mounted relative to the belt spool. With a rotation relative to the belt spool, the coupling disc can bring about a locking of the rotation of the belt spool in unwinding direction of the safety belt. The belt spool has a first friction element ( 22 ) and the coupling disc has a second friction element ( 66 ). The first and second friction elements are positioned such that they are able to connect the belt spool and the coupling disc with each other with a friction fit.

Description:
TECHNICAL FIELD 
   The invention relates to a belt retractor for a vehicle safety belt. 
   BACKGROUND OF THE INVENTION 
   Conventional belt retractors usually have a belt spool mounted rotatably in a frame and a coupling disc rotatably mounted relative to the belt spool, which coupling disc, with a rotation relative to the belt spool, can bring about a locking of the rotation of the belt spool in the unwinding direction of the safety belt. 
   Generic belt retractors, as known for instance from the German Utility Model 201 09 534, serve to provide safety belt band to a vehicle occupant. Normally, the belt band can be withdrawn from the belt spool against the resistance of a spring element. In the blocked state, a withdrawal of belt band is not possible, a differentiation being made basically between two blocking modes. If the blocking takes place as a function of the forces acting on the belt band, then one speaks of belt band-sensitive activation of the locking; if it is determined by the acceleration forces acting on the vehicle, one speaks of vehicle-sensitive activation of the locking. 
   For the belt band-sensitive activation of the locking mechanism of a belt retractor, a coupling disc is arranged on the belt spool so as to be rotatable relative thereto. If the coupling disc, owing to its mass moment of inertia, remains behind the rotation of the belt spool, then through an actuating element it causes the pivoting of a locking catch which thus can be guided into locking teeth. For vehicle-sensitive activation, the coupling disc is provided on its outer periphery with teeth into which a blocking element of a vehicle-sensitive sensor can engage, in order to thus make possible the process of guiding the locking catch into the locking teeth. 
   In order to make possible the renewed retraction of the safety belt, it is necessary to unlock the belt retractor. Whereas the unlocking path with belt band-sensitive locking is already very small, for the unlocking of the vehicle-sensitive locking, a shortening of the unlocking path is desired. According to prior art, in the case of vehicle-sensitive locking, additional components are required for shortening the unlocking path, which lead to increased costs with regard to components and installation. 
   The invention provides a belt retractor by which a drastic shortening of the unlocking path becomes possible after vehicle-sensitive locking on back rotation of the belt spool. 
   BRIEF SUMMARY OF THE INVENTION 
   According to the invention, a belt retractor for a vehicle safety belt comprises a belt spool rotatably mounted in a frame and a coupling disc rotatably mounted relative to the belt spool. With a rotation relative to the belt spool, the coupling disc can bring about a locking of the rotation of the belt spool in unwinding direction of the safety belt. The belt spool has a first friction element and the coupling disc has a second friction element. The first and second friction elements are positioned such that they are able to connect the belt spool and the coupling disc with each other with a friction fit. This friction-fit connection, resulting from the contact of the first and second friction elements, between the belt spool and coupling disc makes it possible that with a necessary unlocking after a vehicle-sensitive locking of the belt retractor, the belt spool directly entrains the coupling disc on its back rotation and therefore ensures that the sensor lever for the vehicle-sensitive locking is freed after a very short back rotation path, whereby the vehicle-sensitive locking can be terminated. With a further back rotation of the belt spool, the locking catch rolls on the locking teeth, so that the actuating element connected with the coupling disc forces a relative movement between belt spool and coupling disc, which leads to the first and second friction elements separating from each other, whereby the friction connection is released and the coupling disc is freed again. This solution does not require any additional components, whereby the component- and installation costs are reduced compared with solutions according to the prior art for shortening the unlocking path. 
   In a preferred embodiment, the first friction element is a pin element and the second friction element is connected elastically with the coupling disc. It is by means of injection molding that the second friction element can be easily formed on the coupling disc and the pin element onto the belt spool. 
   In a further embodiment of the invention, the second friction element has an extension and the belt retractor has a housing element firmly connected with the frame, which element receives the coupling disc. In addition, the housing element has arresting teeth and the extension can come into engagement with the arresting teeth, the belt spool and the coupling disc being able to arrive from a position in which they are connected with each other by friction fit into a position in which they are rotatable relative to each other. Also in this embodiment, the belt spool and coupling disc are firstly connected by friction fit with each other on a back rotation of the belt spool, and the vehicle-sensitive locking is discontinued after a very short back rotation path. On further back rotation of the belt spool, the arresting teeth make it possible that the extension arranged on the second friction element abuts at the arresting teeth, whereby the coupling disc is stopped, the first and second friction elements can reliably be detached from each other, whereby the friction connection between the belt spool and coupling disc is discontinued. 
   Further advantageous developments of the invention will be apparent from the sub-claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an exploded view of the belt retractor according to the invention, 
       FIG. 2  shows a diagrammatic side view of the belt retractor according to the invention, without a coupling disc, 
       FIG. 3  shows a diagrammatic side view, partially in section, of a first embodiment of the belt retractor according to the invention with the locking catch guided into the locking teeth, 
       FIG. 4  shows a diagrammatic side view, partially in section and broken, of the first embodiment of the belt retractor according to the invention, 
       FIG. 5  shows a diagrammatic side view, partially in section and broken, of a second embodiment of the belt retractor according to the invention, with the locking catch partially guided into the locking teeth, and 
       FIG. 6  shows a diagrammatic detailed view, partially in section, of the second embodiment of the belt retractor according to the invention, with the locking catch guided out from the locking teeth. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1 , a belt retractor is illustrated in an exploded view. This has a frame  10 , a belt spool  12 , a locking catch  26 , a coupling disc  32 , a spiral spring  40 , a vehicle-sensitive sensor  46  and a housing element  54 . 
   The belt spool  12  has a spool axle  14 , by which the belt spool is mounted rotatably in the frame  10 . The belt spool comprises a substantially cylindrical spool body  16  and two flanges  18  and  20 , which delimit the spool body  16  to the right and left with respect to  FIG. 1 . A belt band (not illustrated) can be wound on the spool body between the two flanges  18  and  20 . On the right-hand flange  20  of the belt spool  12 , with respect to  FIG. 1 , on the outer side of the belt spool a first friction element  22  and a receiving pocket  24  are arranged, the function of which is explained further below. 
   The locking catch  26  has at least one blocking tooth  28  and a control contour  30 . 
   The coupling disc  32  has a central opening  34 , through which the spool axle  14  of the belt spool  12  can pass, whereby a coaxial connection can be produced between the coupling disc and belt spool. On its outer periphery the coupling disc is provided with control teeth  36 . The coupling disc has in addition an actuating element  38  which can engage into the control contour  30  of the locking catch  26 . 
   The spiral spring  40  comprises a first spring end  42  and a second spring end  44 . 
   The vehicle-sensitive sensor  46  consists of a bearing  48 , a sensor ball  50  movably mounted therein and a sensor lever  52 , which is in contact with the sensor ball and can be moved by the latter. 
   A housing element  54  closes off from the environment the locking catch  26 , coupling disc  32 , spiral spring  40  and vehicle-sensitive sensor  46  and also the region of the flange  20  on the outer side of the belt spool. 
     FIG. 2  shows the belt retractor in a side view, the coupling disc and spiral spring having been removed and the housing element  54  being shown in section. Situated in the frame  10  is a first opening  56 , which is bordered over 360 degrees by locking teeth  58 . Inside the first opening  56 , the region of the flange  20  of the belt spool  12  on the outer side of the belt spool can be seen. On this, a pocket  60  is recessed, on which the locking catch  26  is arranged. The control contour  30  of the locking catch  26  is composed of at least two, here three approximately rectangular recesses, which each are arranged at right angles to each other. The locking catch  26  is mounted in a bearing hole (not illustrated) of the belt spool  12  so as to be pivoting about an axis A perpendicular to the plane of the drawing, and is constructed such that the blocking tooth  28  can be guided into the locking teeth  58 . On the region of the flange  20  on the outer side of the belt spool, there is further provided the first friction element  22 , constructed as a pin element. The vehicle-sensitive sensor  46  is securely mounted on the housing element  54  and is received in the frame  10  by a second opening  62 . 
   In  FIGS. 3 and 4 , the belt retractor is illustrated in side view with coupling disc  32  and spiral spring  40 , with the housing element  54  shown in section. The coupling disc  32  is rotatably mounted on the spool axle  14  of the belt spool  12 . The actuating element  38  is connected via a connecting arm  64  with the coupling disc  32  and engages into the control contour  30  of the locking catch  26 . The first spring end  42  of the spiral spring  40  is arrested close to the spool axle  14  on the coupling disc  32 . The second spring end  44  lies in the receiving pocket  24  of the belt spool  12 , whereby a spring coupling is produced between the coupling disc  32  and the belt spool  12 . If the sensor lever  52 , as in  FIG. 3 , is guided into the control teeth  36 , then the spiral spring  40  usually exerts a rotation force onto the coupling disc, by which the coupling disc is pressed anticlockwise with respect to  FIG. 3  against the sensor lever  52  and the latter is thereby arrested in the control teeth  36 . A second friction element  66  is connected in one piece with the coupling disc  26  and has two sides  66   a  and  66   b  facing the first friction element  22 , by means of which sides  66   a  and  66   b  it can cooperate with the first friction element  22  of the belt spool. The coupling disc  32  additionally has an inertia element  68 , which is formed on the coupling disc  32  via connecting cross-pieces  70 . 
   The unlocking function of the first embodiment of the belt retractor is to be described below. The initial position here is  FIG. 3 , in which the locking catch  26  is guided into the locking teeth  58 . The first friction element  22 , constructed as a pin element, lies here on the first side  66   a  of the second friction element  66 , whereby a friction connection exists between coupling disc  32  and belt spool  12 . Owing to this friction connection, the belt spool  12  entrains the coupling disc  32  on further rotation clockwise with respect to  FIGS. 3 and 4  (arrow a). The friction force of the first friction element  22  on the first side  66   a  must be greater here than the restoring force of the spiral spring  40 , because otherwise the first friction element  22  arrives at the second side  66   b  of the second friction element and the direct contact between belt spool and coupling disc is discontinued, which would bring about a continued arresting of the sensor lever  52  in the control teeth  36 . If the first and second friction elements are in contact with each other, then the sensor lever  52 , through the forced, clockwise rotation of the coupling disc  32  is already freed after a very short rotation path of the belt spool  12  and can swivel out from the control teeth  36 , as illustrated in  FIG. 4  with the aid of the different positions of the sensor lever  52  (movement of the sensor lever in arrow direction b). 
   A further rotation of the belt spool  12  in arrow direction a leads to the blocking tooth  28  of the locking catch  26  rolling on the locking teeth  58 . Thereby, by means of the control contour  30  of the locking catch  26 , a movement is brought about of the actuating element  38 , the latter being connected with the coupling disc  32 . This movement of the actuating element  38  forces a slight displacement of the coupling disc  32  with respect to the belt spool  12  in anticlockwise direction, whereby the first friction element  22  arrives at the second side  66   b  of the second friction element  66 . Thereby, the friction connection is released and the firm coupling between coupling disc  32  and belt spool  12  is discontinued. 
   In a second embodiment, as can be seen in  FIGS. 5 and 6 , the housing element  54  has arresting teeth which are composed of a plurality of tooth elements  74  which lie equidistant on a circle, the central point of which coincides with the spool axle  14 . The angular distance of the tooth elements  74  here is identical both with the angle difference between two teeth of the control teeth  36  of the coupling disc  32  and with that between two teeth of the locking teeth  58  (see circular cutouts K in  FIG. 5 ). The second friction element  66  has an extension  76 , the positions of extension  76  and tooth elements  74  being selected such that the extension can come into engagement with the tooth elements of the arresting teeth, when the first friction element is in the transition region between the two flanks  66   a  and  66   b  of the second friction element. 
   The function of the second embodiment of the belt retractor is described below. In the initial position ( FIG. 5 ) the vehicle-sensitive locking is already discontinued corresponding to the description of the first embodiment, i.e. the sensor lever  52  is no longer retained by the control teeth  36  and can swivel out. On further back rotation of belt spool  12  and coupling disc  32  in arrow direction a, the coupling disc is stopped with the extension  76  on one of the tooth elements  74  of the arresting teeth. As the belt spool  12  can now rotate further clockwise with respect to the coupling disc  32 , the first friction element  22  can move from the first side  66   a  to the second side  66   b  of the second friction element  66 . The friction connection between the first friction element  22  and the second friction element  66  is now released (end position  FIG. 6 ) and the firm coupling between coupling disc  32  and belt spool is discontinued. 
   It is to be understood that the arresting teeth can also be arranged on other fixed parts of the belt retractor, as long as thereby a defined position of the tooth elements  74  is ensured with respect to the second friction element  66  of the coupling disc and therefore with respect to the sensor  46 .