Abstract:
A belt retractor for a seatbelt comprising a retractor pawl which blocks the seatbelt from being pulled out of the belt retractor in the event of an accident, and having a tightening device which tightens the seatbelt in a hazardous situation, the tightening device includes a tightening pawl which, in a blocking position, blocks the belt retractor in the belt uncoiling direction and, in a release position, leaves the belt retractor unaffected. The tightening pawl is assigned a sensor which monitors the position of the tightening pawl and transmits a signal indicating the position of the tightening pawl to a control device of the tightening device.

Description:
BACKGROUND OF THE INVENTION 
   The invention is relates to a belt retractor for a seat belt with a belt reel and a retractor pawl. 
   A conventional belt retractor is disclosed in European Laid-open Specification EP 1 225 105 A2 (incorporated by reference herein). The conventional belt retractor has a retractor pawl which blocks the seatbelt from being pulled out of the belt retractor in the event of an accident. The blocking of the retractor pawl can be initiated, for example, by the fact the seatbelt is pulled out of the belt retractor more rapidly than a predetermined limit speed. In addition, the convention belt retractor has a tightening device which tightens the seatbelt in the event of a hazardous situation. To tighten the seatbelt, the belt reel of the belt retractor is rotated in the belt coiling-up direction, as a result of which the seatbelt is retracted by the belt, retractor and is therefore tensioned. This “tightening position” of the seatbelt is fixed by a tightening pawl which, in a blocking position, is in engagement with a toothed ratchet wheel of the belt retractor and therefore blocks the belt retractor in the belt uncoiling direction. If the tightening device is not active, because, for example, a hazardous situation is not present, then the tightening pawl is brought into a release position in which it is not in engagement with the toothed ratchet wheel of the belt retractor and therefore leaves the belt retractor unaffected. 
   SUMMARY 
   According to an embodiment of the present invention, a belt retractor for a seatbelt includes a belt reel and a retractor pawl which blocks the uncoiling of the seatbelt from the belt reel in the event of an accident, and a tightening device which tightens the seatbelt in a hazardous situation. The tightening device includes a tightening pawl which, in a blocking position, blocks the belt reel in the belt uncoiling direction and, in a release position, leaves the belt reel unaffected. The tightening pawl is assigned a sensor which monitors the position of the tightening pawl and transmits a signal specifying the position of the tightening pawl to a control device of the tightening device 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects, and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below. 
       FIG. 1  shows an exemplary embodiment for a belt retractor according to the present invention in which a tightening pawl blocks a toothed ratchet wheel of the belt retractor. 
       FIG. 2  shows an embodiment according to  FIG. 1 , with the tightening pawl and toothed ratchet wheel being disengaged. 
       FIG. 3  shows an exemplary embodiment for a belt retractor according to the present invention with a Hall sensor and a tightening pawl with a magnetic region, in which the tightening pawl blocks a toothed ratchet wheel of the belt retractor. 
       FIG. 4  shows another embodiment of a belt retractor with a retractor pawl and an optical sensor, in which a tightening pawl and toothed ratchet wheel are disengaged. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a belt retractor  10  whose retractor pawl and whose belt reel for retracting the seatbelt are not shown for the sake of clarity.  FIG. 1  illustrates a toothed ratchet wheel  20  which is connected in a rotationally fixed manner to the belt reel of the belt retractor  10 .  FIG. 3  illustrates the belt reel R and seatbelt  5 .  FIG. 4  illustrates an exemplary retractor pawl  120 . 
   A tightening pawl  30  is connected to the toothed ratchet wheel  20  in such a manner that the toothed ratchet wheel  20  can be rotated exclusively along the belt coiling-up direction  40 . The toothed ratchet wheel  20  cannot be moved in the belt uncoiling direction, i.e. counter to the arrow direction of the arrow  40 , owing to the blocking position of the tightening pawl 
   It can be seen in  FIG. 1  that the teeth of the toothed ratchet wheel  20  and the tightening pawl are designed in such a manner that they form a form-fitting connection on account of an undercut. Owing to this form-fitting connection, the tightening pawl  30  cannot readily be brought from its blocking position, which is illustrated in  FIG. 1 , into a release position in which it would be disengaged from the toothed ratchet wheel  20 . 
   As can furthermore be seen in  FIG. 1 , the tightening pawl  30  is mechanically connected to an electromagnet  50  which is activated by a control device  60 . In addition, there is a restoring spring  70  between the tightening pawl  30  and the electromagnet  50 , the restoring spring likewise acting on the tightening pawl  30 . 
   The electromagnet  50  is connected to the tightening pawl  30  in such a manner that the tightening pawl  30  can be brought by the electromagnet  50  into the blocking position illustrated in  FIG. 1 ; for this purpose, the electromagnet  50  has to be activated, i.e. brought into the “attracted” state. As soon as the tightening pawl  30  has come into engagement with the toothed ratchet wheel  20 , the blocking position of the tightening pawl  30  is fixed on account of the form-fitting connection with the toothed ratchet wheel  20 . Even after the electromagnet  50  is switched off, the tightening pawl  30  cannot therefore be transferred into a release position before the form-fitting connection is cancelled. 
   However, as soon as the form-fitting connection is cancelled, the restoring force of the restoring spring  70 , which is tensioned by the electromagnet  50 , will act on the tightening pawl  30  and will pivot the tightening pawl  30  from the blocking position into a release position, specifically about the pivot axis  80 . For this purpose, the restoring spring  70  is fitted between the tightening pawl  30  and the electromagnet  50 . 
     FIG. 1  furthermore illustrates a sensor  100  which is connected to the control device  60  via feed lines  110 . 
   The particular position of the tightening pawl  30  can be determined with the sensor  100 ; it can therefore be determined whether the tightening pawl  30  is in its blocking position or in its release position. 
   If the tightening pawl  30  is now to be transferred from its blocking position, which is illustrated in  FIG. 1 , into a release position, then first of all the toothed ratchet wheel  20  has to be rotated along the belt coiling-up direction  40  until the toothed ratchet wheel  20  and the tightening pawl  30  lose their form-fitting connection and can be disengaged. As soon as this is the case, the spring force of the restoring spring  70  causes the tightening pawl  30  to be pivoted about its pivot axis  80  and therefore to be disengaged from the toothed ratchet wheel  20 . 
   The position of the tightening pawl  30  after being pivoted about the pivot axis  80  is shown in  FIG. 2 . It can be seen that the sensor  100  makes it possible to establish the position of the tightening pawl  30 . 
   If the tightening pawl  30  is in its blocking position, then a corresponding “blocking position” signal is transmitted to the control device  60  by the sensor  100 ; if, in contrast, the tightening pawl  30  is in its release position, then a corresponding “release” signal indicating the release position is transmitted by the sensor  100  to the control device  60 . 
   As a function of the control signal transmitted by the sensor  100 , the control unit  60  decides on the manner in which the electromagnet  50  and/or the driving motor of the belt retractor have to be activated. The examples of the operating modes which the control device  60  can make possible will now be summarized in brief. 
   The operation of the retractor for tightening the seat belt will now be described. According to an embodiment, the control device  60  will first of all activate a drive of the belt retractor via a control line (not illustrated in  FIGS. 1 and 2 ) in such a manner that the belt reel is rotated along the belt coiling-up direction  40 , to tighten the seatbelt. This rotation of the belt reel along the belt coiling-up direction  40  causes the seatbelt to be tightened, so that the seat belt bears firmly against the vehicle occupant. At the same time or shortly afterwards, the control device  60  will activate the electromagnet  50  in such a manner that the tightening pawl  30  comes into engagement with the toothed ratchet wheel  20 . In this case, the tightening pawl  30  always comes into engagement with the toothed ratchet wheel  20  upstream of the retractor pawl, with the result that the tightening pawl  30  is load-bearing. Should the tensile force acting on the seatbelt in the belt pull-out direction exceed a predetermined maximum value, the rotationally fixed connection between the belt reel and the toothed ratchet wheel  20  would be broken open or cancelled—for example by a torque transmission pin shearing off—and the belt reel could rotate again. Thereupon the preset retractor pawl in the belt retractor housing or frame would then become load-bearing. 
   If, however, the tightening pawl  30  is still load-bearing—i.e. before the rotationally fixed connection between the belt reel and the toothed ratchet wheel  20  “breaks open” in the event of an “overload”—and engages in the toothed ratchet wheel  20 , its “blocking position” is fixed owing to the form-fitting connection with the toothed ratchet wheel  20 ,  50  that in spite of the restoring force of the “tensioned” restoring spring  70 , the tightening pawl  30  cannot pivot back into the release position illustrated in  FIG. 2 . 
   Owing to the blocking position of the tightening pawl  30 , neither the toothed ratchet wheel  20  nor the belt reel of the belt retractor  10 , which reel is connected in a rotationally fixed manner to the toothed ratchet wheel  20 , can rotate in the belt uncoiling direction—i.e. counter to the arrow direction  40  according to  FIG. 1 , with the result that the seatbelt bears firmly against the vehicle occupant and is fixed in this position. 
   The release of the retractor&#39;s locking mechanism will now be described. According to an embodiment, if the control device  60  ascertains by means of sensors (not illustrated in  FIGS. 1 and 2 ) that there is no longer a hazardous situation and the seatbelt may be released, the tightening pawl  30  is to be pivoted from its blocking position illustrated in  FIG. 1  into the release position illustrated in  FIG. 2 . Since a pivoting movement of this type is not readily possible on account of the form-fitting connection between the tightening pawl  30  and the toothed ratchet wheel  20 , the control device  60  has to activate the driving motor of the belt retractor  10  in such a manner that the belt reel and the toothed ratchet wheel  20  are rotated—if only slightly—along the belt coiling-up direction  40 , so that the toothed ratchet wheel  20  and the tightening pawl  30  can be disengaged. As soon as the tightening pawl  30  is no longer held by the toothed ratchet wheel  20 , the restoring force of the restoring spring  70  will cause the tightening pawl  30  to pivot away about the pivot axis  80  and pass into the release position illustrated in  FIG. 2 . This “springing back” of the tightening pawl  30  into the release position according to  FIG. 2  is ascertained by the sensor  100  which passes on a corresponding “release position” signal to the control device  60 . The control device  60  thereupon knows that further activation of the driving motor of the belt retractor  10  is no longer required and the belt reel and the toothed ratchet wheel  20  no longer have to be rotated along the belt coiling-up direction  40 . A corresponding activation of the driving motor is therefore immediately switched off. Owing to the driving motor being immediately switched off, it is ensured that, in order to deactivate the tightening pawl  30 , the toothed ratchet wheel  20  and the belt reel have to be rotated in the belt coiling-up direction  40  merely to the extent absolutely necessary. 
   The position of the tightening pawl  30  during a hazardous situation may be monitored as described below. According to an embodiment, the control device  60  may monitor whether the tightening pawl  30  is in the correct position, i.e. in the blocking position, during the continuation of a hazardous situation. In specific terms, the sensor  100  is continuously monitored by the control device  60 , and it is continuously determined which position the tightening pawl  30  is in. If it is ascertained during this monitoring of the sensor  100  that the tightening pawl  30  has been released and transferred into its release position owning to the restoring force of the restoring spring  70 , then, by renewed activation of the electromagnet  60 , the control device  60  can bring the tightening pawl  30  into the blocking position again. Owing to the combination of the control device  60  with the sensor  100 , it is therefore possible, even during the continuation of a hazardous situation, to ensure that the blocking pawl  30  is always in the required blocking position. 
   The seatbelt may be retightened. For example, if the vehicle occupant is not in the correct sitting position during a first tightening process, then despite the tightening which has taken place by means of the tightening device, the seatbelt may not lie correctly or the vehicle occupant may not have been pulled completely back into the seat. In an embodiment, if, after a first tightening, the seatbelt still has slack, then the restoring spring which is present in the belt retractor  10  will rotate the belt reel and therefore the toothed ratchet wheel  20  along the belt coiling-up direction  40 . Owing to this rotation, the previous form-fitting connection between the toothed ratchet wheel  20  and the tightening pawl  30  will be released, whereupon the restoring spring  70  will transfer the tightening pawl  30  into the released position. The sensor  100  will ascertain this behavior of the tightening pawl  30  and transmit a corresponding signal to the control device  60 . The control device  60  thereupon recognizes that the seatbelt is no longer tightened and will thereupon activate the driving motor of the belt retractor  10  in such a manner that the belt reel is rotated along the belt coiling-up direction  40  and the seatbelt is coiled up. After the associated, renewed tightening of the seatbelt, the control device  60  will activate the electromagnet  50  a further time in such a manner that the tightening pawl  30  is transferred into the blocking position and passes into a form-fitting engagement with the toothed ratchet wheel  20 . In summary, it is therefore possible with the control device  60  and the sensor  100  to also recognize an insufficient first tightening and to correct it in a second tightening step following thereupon. 
   The sensor, which is illustrated in  FIGS. 1 and 2 , may be, for example, a Hall sensor  100   a  which interacts with the tightening pawl  30 ; for this purpose, at least part of the tightening pawl  30  has a magnetic region  30   a  which can be recognized by the Hall sensor  100   a.    
   Instead of a Hall sensor the sensor may also be an optical sensor  100   b  which forms a light barrier, for example, in order to determine the position of the tightening pawl  30 . 
   Moreover, as has been explained in conjunction with  FIGS. 1 and 2 , the sensor  100  and the control device  60  may also be used in other designs of belt retractor. For example, reference may be made in this connection in particular to a belt retractor which is shown in FIGS. 1 to 11 of European Laid-open Specification EP 1 225 105 A2 and is described in detail in the passage from column 8, line 55 to column 15, line 40 (hereby incorporated by reference herein in its entirety). Reference may be made to the explanations given there in respect of the manner of functioning of this belt retractor. 
   In addition, the sensor  100  and the control device  60  may also be used, for example, in the case of a belt retractor as is described in detail in conjunction with FIG. 12 and the passage from column 15, line 41 to column 16, line 18 of the abovementioned European laid-open specification. 
   Of course, the tightening device described with reference to the exemplary embodiment and having the sensor  100  and the control device  60  may also be used in all other known types of belt retractor. 
   Accordingly, provision is made according to an embodiment of the invention for the tightening pawl to be assigned a sensor which monitors the position of the tightening pawl and transmits a signal specifying the position of the tightening pawl to the tightening device. 
   An advantage of an embodiment of the belt retractor can be seen in the fact that the activation of the tightening pawl by the tightening device is significantly improved and simplified owing to the presence of the sensor. It is thus namely possible to use the sensor to determine the particular position of the tightening pawl and therefore to ascertain whether the tightening pawl is in the desired position, for example, in the blocking position. If this is not the case, appropriate activation of the tightening pawl enables the error to be eliminated and the tightening pawl to be brought into the desired position. 
   Another advantage of an embodiment of the belt retractor can be seen in the fact that with it greater comfort is achieved for the vehicle occupant than would be the case without a sensor. In order to unlock the tightening pawl, it is namely necessary for the belt retractor to be rotated—at least slightly—in the belt coiling-up direction in order to disengage the tightening pawl and a toothed ratchet wheel (or the like) of the belt retractor, which wheel is in engagement with the tightening pawl. With the sensor provided according to the invention, the position in which the tightening pawl is in can now be monitored, so that, during the unlocking of the tightening pawl, the belt reel of the belt retractor has to be rotated in the belt coiling-up direction only to the extent absolutely necessary in order to make it possible for the tightening pawl to change over from the blocking position into the release position. The sensor according to an embodiment of the invention is highly advantageous here, in particular, if the tightening pawl and the toothed ratchet wheel form a form-fitting connection—for example by means of an undercut—and therefore cannot readily be separated from each other; this is because, in this case, the sensor can be used to monitor the time from which the tightening pawl and the toothed ratchet wheel are no longer in engagement and are separated. 
   Another advantage of an embodiment of the belt retractor can be seen in the fact that it is also able to be used to recognize when the vehicle occupant has not been pulled back completely into the seat during a first tightening process of the tightening device and the seatbelt therefore still has play or is still loose. In such a case, the restoring spring which is always present in the belt retractor will namely pull the seatbelt back, as a result of which the blocking pawl is, if appropriate, transferred “unintentionally” from its blocking position into the release position. This—unintentional—switching over of the tightening pawl into the release position can be detected by the sensor provided according to the invention, so that the desired tightening of the seatbelt can be brought about in a subsequent “second” tightening process. In other words, the effect which can be achieved in an embodiment of the belt retractor owning to the presence of the sensor is that the seatbelt is also tightened repeatedly until the belt is tightened as desired. 
   The belt reel can be locked in a particularly simple and therefore advantageous manner with the aid of the tightening pawl when the belt retractor has a toothed ratchet wheel which is connected in a rotationally fixed manner to the belt reel and interacts with the tightening pawl. 
   In order to achieve the effect that the tightening pawl remains in its blocking position even if the drive acting on the tightening pawl in order to change over the position of the latter is switched off, it is regarded as advantageous if, in its blocking position, the tightening pawl forms a form-fitting connection with at least one tooth of the toothed ratchet wheel. 
   The form-fitting connection can be formed, for example, by an undercut. 
   It is regarded as advantageous if the tightening pawl is connected to a restoring device which automatically separates the tightening pawl from the toothed ratchet wheel as soon as there is no longer a form-fitting connection between the tightening pawl and the toothed ratchet wheel. The effect achieved in this advantageous refinement of the belt retractor is that the tightening pawl is automatically separated from the toothed ratchet wheel as soon as the belt reel of the belt retractor and therefore the toothed ratchet wheel are rotated in the belt coiling-up direction. 
   The restoring device can be formed in a particularly simple and advantageous manner by a restoring spring, for example. 
   Moreover, it is regarded as advantageous if the tightening device is designed in such a manner that it rotates the belt reel of the belt retractor in the coiling-up direction to release the blocking position of the tightening pawl. As has already been explained, this is because, when the belt reel is rotated in the coiling-up direction, the tightening pawl and the toothed ratchet wheel are disengaged, whereupon the restoring device can automatically transfer the tightening pawl from the blocking position into the release position. 
   In order to increase the comfort for a vehicle occupant protected by the seat belt, it is regarded as advantageous if as small a tightening force as possible is exerted on the seatbelt in order to unlock the tightening device. In order to achieve this, provision is made, according to a development of the belt retractor, for the tightening device to rotate the belt reel exclusively in the belt coiling-up direction until the sensor produces a signal which indicates the release position of the tightening pawl. In this refinement of the invention, the restoring device and the sensor operate “hand in hand” with each other, and so, namely during a rotation of the belt reel in the belt coiling-up direction, the toothed ratchet wheel and the tightening pawl are disengaged, whereupon the restoring device automatically transfers the tightening pawl from the blocking position into the release position; this transfer from the blocking position into the release position is in turn detected by the sensor which passes on a corresponding signal to the tightening device which then commences the further tensioning of the seat belt for the purpose of unlocking the tightening pawl. 
   Moreover, it is regarded as advantageous if the tightening device is designed in such a manner that it continuously monitors the position of the tightening pawl with the sensor during the presence of a hazardous situation. With continuous monitoring of the position of the tightening pawl, it can namely be ensured that the said tightening pawl cannot pass unnoticed from the blocking position into the release position and release the seat belt. 
   In respect of monitoring the tightening pawl, it is regarded as advantageous if the tightening device is designed in such a manner that it repeats, appropriate, the tightening process of the seatbelt if the sensor signals the release position of the tightening pawl although the hazardous situation has not yet ended. 
   A particularly simple and cost-effective sensor is, for example, a Hall sensor, with the result that it is regarded as advantageous if the tightening pawl is at least partially magnetic and the sensor is formed by a Hall sensor. 
   As an alternative, other types of sensor are also conceivable; thus, the sensor may be, for example, an optical sensor which, for example forms an optical light barrier for “measuring” or determining the position of the tightening pawl. 
   Moreover, the sensor can also be formed by an electrical switching contact, the switching state of which indicates whether the tightening pawl is situated in the blocking position or in the release position. 
   The priority application, DE 103 10 019.9, filed Feb. 28, 2003, is incorporated by reference herein in its entirety. 
   Given the disclosure of the present invention, one versed in the art would appreciate that there may be other embodiments and modifications within the scope and spirit of the invention. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is to be defined as set forth in the following claims.