Abstract:
A buckle tensioner for pre-tensioning a safety belt band comprises a traction transmission device engaging on a belt buckle, a motor and a pressure storing device which is able to be compressed by means of the motor. The traction transmission device is coupled in a force-fitting manner to the pressure storing device and the pressure storing device is arranged such that an expansion of the pressure storing device brings about a pulling away of the belt buckle for tensioning the safety belt band.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates to a buckle tensioner for pre-tensioning a safety belt band.  
         BACKGROUND OF THE INVENTION  
         [0002]    Conventional buckle tensioners have a traction transmission device engaging on a belt buckle, a motor and a pressure storing device which is able to be compressed by means of the motor.  
           [0003]    Such a buckle tensioner is known from the DE 199 61 799. In this reversible buckle tensioner, an electromotive drive provides for a pre-tensioning of the safety belt band in the case of an inuninent accident, by a piston of the tensioner drive, coupled to a belt buckle, being brought into an intermediate position. If a collision does not take place, the piston is returned into its initial position by a compression spring, so that the belt buckle is situated in its normal position again.  
           [0004]    The invention provides a buckle tensioner which makes possible a reliable, reversible pre-tensioning with favorably priced components.  
         BACKGROUND OF THE INVENTION  
         [0005]    According to the invention, a buckle tensioner for pre-tensioning a safety belt band comprises a traction transmission device engaging on a belt buckle, a motor and a pressure storing device which is able to be compressed by means of the motor. The traction transmission device is coupled in a force-fitting manner to the pressure storing device and the pressure storing device is arranged such that an expansion of the pressure storing device brings about a pulling away of the belt buckle for tensioning the safety belt band. In contrast to the known buckle tensioner, the motor is not used for the actual pre-tensioning process, but rather serves for the previous compression of the pressure storing device. The expansion of the pressure storing device is used for the pre-tensioning process. As the compression of the pressure storing device is non-critical with respect to time and only has to be repeated possibly after an actual pre-tensioning process, a simple motor can be used for this. The only prerequisite is that the motor provides the torque necessary for compressing the pressure storing device. The pressure storing device preferably comprises a helical spring, but a pressure storing device which works with a compressible fluid (pneumatic or hydraulic pressure reservoir) can also be used.  
           [0006]    The motor is preferably constructed so as to be self-locking, so that after the compression of the pressure storing device by the motor, no further steps are necessary in order to keep the pressure storing device in its compressed state. Alternatively, however, the pressure storing device can also be kept in a compressed state by a locking device.  
           [0007]    In the preferred embodiment of the invention, the expansion of the pressure storing device is brought about by a trigger device which is able to be activated by the motor. Therefore, the motor has a dual function: Firstly, it is used for compressing the pressure storing device, to set the buckle tensioner into the state ready for operation; secondly, if required in a precrash situation, it activates the trigger device. This saves additional components which would otherwise be necessary for triggering the pre-tensioning process.  
           [0008]    Preferably the pressure storing device is compressed by means of a longitudinally displaceable first rack, driven by the motor. According to the preferred embodiment of the invention, the motor is coupled to a pinion which engages into first teeth of the first rack, the latter being brought out of engagement with the pinion by activation of the trigger device. Thus, the compressed pressure storing device can be released in a simple manner to carry out the pre-tensioning process.  
           [0009]    A particular advantage is produced in that the trigger device comprises a trigger piece movably supported on the first rack and coupled to a second rack having teeth which are constructed so as to be complementary to second teeth of the first rack, the second teeth of the first rack being brought into engagement with the teeth of the second rack on activation of the trigger device, and the racks being arranged such and the profiles of the teeth of the racks being constructed such that a relative displacement of the second rack with respect to the first rack brings the first teeth of the first rack into engagement with the pinion again. Such a construction makes it possible after a pre-tensioning process to return the tensioner mechanism in a simple manner into a state in which the pressure storing device can be compressed again, so that the buckle tensioner is available for a further pre-tensioning process.  
           [0010]    For the emergency tensioning, following the pre-tensioning in an actual accident, according to a further development of the invention a pyrotechnic device is provided, which is coupled to the buckle tensioner such that through the pyrotechnic device a further tensioning is achieved which goes beyond that obtained through the expansion of the pressure storing device. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 shows a lateral sectional view of a buckle tensioner according to the invention;  
         [0012]    [0012]FIG. 2 shows an enlarged sectional view of the tensioner of FIG. 1 along the line A-A;  
         [0013]    [0013]FIGS. 3 a - 3   f  show partial views in section of the buckle tensioner of FIG. 1 in various phases of the buckle tensioning; and  
         [0014]    [0014]FIG. 4 shows a lateral sectional view of a further development of the buckle tensioner according to the invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    The buckle tensioner illustrated in FIG. 1 comprises a belt buckle  10 , to the lower end of which a first end of a rigid traction cable  12  is coupled. The traction cable  12 , running obliquely downwards, is guided over a deflection device  14  in a horizontal direction parallel to the vehicle floor. In this horizontal direction, adjoining the deflection device  14  is an elongated, cylindrical tube  16  into which the traction cable  12  is introduced. At the front end of the tube  16 , facing the deflection device  14 , the front end of a helical spring  18  rests, which is coupled to the traction cable  12  in a force-fitting manner. The rear end of the helical spring  18  rests against a support ring  20 , which is firmly connected with a first rack  22  arranged in the tube  16 . In an alternative embodiment, the support ring  20  is constructed in one piece with the rack  22 .  
         [0016]    The first rack  22  is held in the tube so as to be both longitudinally displaceable and also vertically movable. A central part  24  of the first rack  22  (see FIG. 2) has upper and lower teeth, the upper teeth  26  being closely spaced and having a symmetrical profile, whereas the lower teeth  28  are spaced further apart and have an asymmetrical profile with a steeply rising flank on one side and a slightly falling flank on the other side. A rear section of the toothed central part  24  (designated below as trigger piece  30 ) is held so as to be longitudinally displaceable between an end piece  32  of the first rack  22  and the front section  34  of the central piece  24 , and is prestressed by a first spiral spring  36  towards the end piece  32 . Underneath the first rack  22 , a second rack  38  is arranged with an upwardly pointing toothing, the teeth  40  of which are constructed so as to be complementary to the lower teeth  28  of the first rack  22 . The front end of the second rack  38 , facing the support ring  20 , lies against a second spiral spring  42  which rests on the side of the support ring  20  facing away from the helical spring  18 . An upwardly extending extension  44  in the rear region of the second rack  38  projects between the front section  34  of the central piece  24  and the trigger piece  30  of the first rack  22 . The trigger piece  30  with the first spiral spring  36  and the second rack  38  together form a trigger device, the function of which is explained further below with the aid of FIGS. 3 a - 3   f.    
         [0017]    A pinion  46 , which is driven by a direct-current motor and is non-rotatably coupled to the motor shaft thereof, engages into the upper teeth  26  of the first rack  22 . Therefore, the first rack  22  can be displaced in longitudinal direction. At a predetermined location on the tube  16  a sensor  50  is arranged, which detects a passing of the support ring  20 .  
         [0018]    The mode of operation of the buckle tensioner is described below with the aid of FIGS. 3 a - 3   f.  In order to reach the normal state of the buckle tensioner with the helical spring  18  being in the pre-stressed state (shown in FIG. 3 a ), the first rack  22  is pushed to the left against the force of the helical spring  18  by a clockwise rotation of the pinion  46  until the sensor  50  registers the passing of the support ring  20  and the motor  48  is then switched off. During the pre-stressing, the two racks  22 ,  38  do not mesh with each other, but rather the lower teeth  28  of the first rack  22  lie on the teeth  40  of the second rack  38 . Due to the extension  44  lying against the trigger piece  30 , however, the second rack  38  is also displaced with the first rack  22 . On completion of the motor movement, the pinion  46  is only in engagement with the teeth  26  of the trigger piece  30 . The racks  22 ,  38  remain in the position shown in FIG. 3 a,  because the motor  48  locks and hence the immovable pinion  46  prevents a pushing back of the first rack  22 .  
         [0019]    Alternatively, a locking of the support ring  20  can also be provided, for example by means of a catch engaging into a recess of the tube  16 . FIGS. 3 b  and  3   c  show the unlocking phase of the tensioner mechanism before an imminent accident. The motor  48  turns the pinion  46  clockwise, until the trigger piece  30  has displaced the second rack  38  to the left against the force of the two spiral springs  36 ,  42  approximately by half the width of a tooth  28  or  40 . From the forces transferred by the pinion  46  and the helical spring  18  to the first rack  22 , a downwardly directed force component is also produced. Therefore, owing to the relative position of the teeth  28  and  40  with respect to each other, the first rack  22  can move downwards until the teeth  28 ,  40  engage fully into each other and the first rack  22  is out of engagement with the pinion  46 .  
         [0020]    Through the release of the first rack  22  the helical spring  18 , which is coupled to the traction cable  12 , will expand abruptly, so that the belt buckle  10  is pulled away obliquely downwards. When, after the pre-tensioning is completed, the two racks  22 ,  38  displaced towards the right have reached the end position shown in FIG. 3 d,  the second spiral spring  42  forces the second rack  38  further towards the right. Owing to the special profile of the teeth  28  and  40  and of the special mechanism including the movably supported trigger piece  30  and the first spiral spring  36 , which counteracts a displacement of the first rack  22  towards the right, an upwardly directed force onto the first rack  22  is produced. The first rack  22  is thereby forced upwards, until it is in engagement with the pinion  46  again and the lower teeth  28  lie opposite the teeth  40  of the second rack  38  (see FIGS. 3 e  and  3   f ). By further rotation of the pinion  46  in a clockwise direction, the helical spring  18  can be compressed again and the buckle tensioner mechanism can be brought again into the initial position shown in FIG. 3 a.    
         [0021]    In FIG. 4, a further development of the buckle tensioner according to the invention is shown, in which in addition a pyrotechnic device  52  is provided for emergency tensioning. If a severe impact does in fact occur after the pretensioning, a pyrotechnic charge  54  is ignited and the gas which is thereby provided and introduced into the tube  16  brings about an additional tensioning, i.e. the belt buckle  10  is pulled away further downwards.  
         [0022]    From the above description, it can be seen that as motor  48  a simple brush motor with only one direction of rotation can be used. As an alternative to the helical spring  18 , a pneumatic or hydraulic pressure reservoir can also be used with a compressible fluid whereby, however, the mode of operation of the tensioner mechanism is not altered. The terms “upper” and “lower” used in the description (e.g. upper and lower teeth) and also “left” and “right” were selected for a clear description of the preferred embodiments according to the illustration in the figures, but are in no way to be understood as being restrictive.