Patent Publication Number: US-2005127228-A1

Title: Belt retractor for a vehicle safety belt

Description:
The invention relates to a belt retractor for a vehicle safety belt.  
     BACKGROUND OF THE INVENTION  
      Conventional belt retractors for a vehicle safety belt comprise a frame, a belt reel, a locking pawl which can be caused to engage in a locking toothing in order to stop the belt reel from rotating in the frame, and a control mechanism by which the locking pawl can be caused to engage in the locking toothing in a vehicle-sensitive and/or belt-sensitive manner.  
      A belt retractor of this type is well known. The control mechanism arrests the belt reel either in a vehicle-sensitive manner, i.e., when the accelerations acting on the vehicle exceed a preestablished value, or in a belt-sensitive manner, i.e., when the rotational acceleration of the belt reel, caused by a rapid unwinding of the belt from the belt reel, exceeds a preestablished value. The control mechanism usually contains a coupling disk, which functions to activate both the belt-sensitive as well as the vehicle-sensitive locking action of the belt reel. Basically, the locking of the belt reel is brought about by a relative rotation between the coupling disk and the belt reel. This relative rotation is exploited to cause the locking pawl to engage in the locking toothing. In the case of vehicle-sensitive locking, the coupling disk is engaged by a sensor that is usually attached to the frame of the belt retractor, so that when the belt is unwound from the belt reel, the coupling disk that is held fast by the sensor lags behind the rotation of the belt reel. In the case of belt-sensitive locking, the mass inertia of the coupling disk is exploited so that the coupling disk lags behind compared to the rotation of the belt reel. Here too, the relative rotation between the coupling disk and the belt reel is exploited to cause the locking pawl to engage in the locking toothing.  
      The objective of the invention lies in improving a belt retractor of the type cited above such that the belt-sensitive and the vehicle-sensitive locking of the locking pawl can be achieved with smaller tolerances than heretofore.  
     BRIEF DESCRIPTIONS OF THE INVENTION  
      For this purpose, the invention provides a belt retractor having a frame, a belt reel, a locking pawl which can be caused to engage in a locking toothing in order to stop the belt reel from rotating in the frame, and a control mechanism by which the locking pawl can be caused to engage in the locking toothing in a vehicle-sensitive and/or belt-sensitive manner. The control mechanism has an inertial disk and a cam disk, which are coupled to the locking pawl independently of each other. The basic idea of the invention is to functionally decouple vehicle-sensitive locking from belt-sensitive locking. In this way, any type of control mechanism can be executed more precisely.  
      Advantageous embodiments of the present invention will become apparent from the subclaims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention is described below on the basis of a preferred embodiment, which is depicted in the attached drawings. In the latter:  
       FIG. 1  in a perspective exploded view depicts a belt retractor according to the present invention;  
       FIG. 2  depicts a schematic view of the control mechanism used in the belt retractor in  FIG. 1 ;  
       FIG. 3  depicts a schematic top view of the control mechanism, the cam disk being emphasized; and  
       FIG. 4  depicts a schematic top view of the control mechanism, the inertial disk being emphasized.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      In  FIG. 1 , a belt retractor is depicted, which has a frame  10  in which a belt reel  12  is rotatably attached. A safety belt (not shown) is carried on the belt reel.  
      On one end face of belt reel  12 , a locking pawl  14  is attached in a manner that permits it to swivel. Locking pawl  14 , beginning from a resting position in which its free end essentially does not extend beyond the external periphery of the belt reel, can be swiveled in the radial direction to the outside into a locking position, in which it engages in a locking toothing  16  provided on frame  10 . In this state, belt reel  12  relative to the frame is prevented from rotating in the direction in which the belt is unwound.  
      A control mechanism  18  is provided, which is made up of a cam disk  20 , an inertial disk  22 , and a sensor  24 . These parts are arranged within a cover  26 , sensor  24  being fixedly attached to cover  26  and therefore fixed relative to frame  10  of the belt retractor.  
      Cam disk  20  (also see  FIG. 2 ) is rotatably attached on an axle  28  of belt reel  12 . On its exterior side, it has a control toothing  30 , in which a control pawl  32  of sensor  24  can be caused to engage, the control pawl in turn being activated by an inertial ball  34 .  
      Inertial disk  22  is rotatably supported on a collar  36  of cam disk  20 . Both cam disk  20  as well as inertial disk  22  each have a slot which cooperates with a pin  40 , that is attached to locking pawl  14 .  
      The configuration of cam disk  20  will now be described with reference to  FIG. 3 . Cam disk  20  has a slot which is composed of a first cam surface  42  and a second cam surface  44 . The two cam surfaces are disposed at an angle to each other such that a triangle results that is open to the outside. Pin  40  of locking pawl  14  cooperates with both cam surfaces  42 ,  44 . Apart from the indirect coupling via pin  40  and locking pawl  14 , cam disk  20  can rotate freely relative to belt reel  12 .  
      The configuration of inertial disk  22  will now be described with regard to  FIG. 4 . Inertial disk  22  has a comparatively high mass inertia; in particular, it can be made of metal or of plastic with metal inserts. Inertial disk  22  has a slot  46 , which is executed as an elongated slot that runs in a straight line. The longitudinal axis of this slot, viewed with regard to the rotational direction of the belt reel when the belt is being unwound (indicated by the arrow P), lags behind the rotational axis of the belt reel. A spring  48  is provided, which is configured here as a tension spring and acts between belt reel  12  and a buttress  50  on inertial disk  22 . Spring  48  urges inertial disk  22  in the same direction in which the belt reel rotates when the belt is being unwound.  
      In the resting position, i.e., when no excessively high accelerations are acting upon the belt retractor and the belt reel, the control mechanism is in the state depicted in  FIGS. 3 and 4 . Control pawl  32  of sensor  24  does not engage in control toothing  30  of cam disk  20 , so that the cam disk can rotate freely. In addition, spring  48  urges inertial disk  22 , with regard to  FIGS. 3 and 4 , in a counterclockwise motion, so that slot  46  acts upon pin  40  also in a counterclockwise motion. In this manner, locking pawl  14  is urged into its resting position, i.e., in its position that is swiveled radially to the inside. The resting position is defined as that in which pin  40  contacts both cam surfaces  42 ,  44  of cam disk  20 . In this way, the angular orientation of cam disk  20  in its resting position is precisely defined.  
      When the vehicle-sensitive locking is activated, control pawl  32  is caused to engage in control toothing  30  of cam disk  20 . When the belt is then unwound from the belt reel, a relative rotation is generated between belt reel  12  and cam disk  20 ; in the representation in  FIG. 3 , belt reel  12  is rotated in a counterclockwise motion whereas cam disk  20  remains stationary. In this manner, locking pawl  14 , with respect to the representation in  FIG. 3 , is pushed upwards; in this context, pin  40  rides up onto first cam surface  42 , as a result of which locking pawl  14  is pivoted about its swivel-and-support point S in a clockwise fashion, so that its free end is radially moved to the outside and is caused to engage in locking toothing  16 . When locking pawl  14  is radially swiveled to the outside, due to the constrained guidance of pin  40  of locking pawl  14  in slot  46  of inertial disk  22 , inertial disk  22  rotates slightly relative to belt reel  12 ; however, this does not have any influence on the vehicle-sensitive locking process.  
      In a belt-sensitive locking, in the same manner as in the case of vehicle-sensitive locking, belt reel  12  rotates with respect to  FIGS. 3 and 4  in a counterclockwise motion. In this context, pin  40  of locking pawl  14  rides up on the upper flank of slot  46  in inertial disk  22 . Because this flank runs in a diagonal direction, pin  40  is pushed upwards, as a result of which locking pawl  14  is caused to engage to the outside in locking toothing  30 . When locking pawl  14  is swiveled, its pin  40  moves away from cam surfaces  42 ,  44  of the slot formed in cam disk  20 , so that the process of engaging locking pawl  14  is no longer influenced by the cam plate.  
      As soon as the belt reel experiences the slightest reverse rotation, i.e., a rotation in the direction of winding up the belt, spring  48  sets the control mechanism once again in its resting position, in which locking pawl  14  is rotated radially to the inside. Belt reel  20  is then able once again to rotate freely.  
      The belt retractor described has the following advantages: The position of the cam disk can be more precisely determined without as a result causing friction to act on the inertial disk. As a result, contact between control pawl  32  of sensor  24  and cam disk  20  occurs in a more reliable manner. In addition, in response to a protracted vehicle-sensitive locking, control pawl  32  is more reliably engaged with cam disk  20 . In vehicle-sensitive activation, locking pawl  14  is engaged in locking toothing  16  without any delay, i.e., without any free traveling. With regard to inertial disk  22 , the demands for determining its position are less stringent because the inertial disk has no functional interface with sensor  24 . In addition, the guidance surfaces for inertial disk  22  can be arranged close to the rotational axis of the belt reel, so that bearing friction torques and therefore the influence exerted on belt-sensitive locking is minimal.