Abstract:
A belt tightener of a seat belt in a vehicle, in particular a motor vehicle, is provided with a retracting spring in order to return the belt. A counterspring, which can be adjusted by a motor, is connected in parallel with the retracting spring in order to be able to reduce the tensile force of the belt for comfort considerations. The motor can also be connected in drive terms to the belt via a coupling arrangement to give reversible belt tightening.

Description:
[0001]    This application claims the priority of German application 101 58 871.2, filed Nov. 30, 2001, the disclosure of which is expressly incorporated by reference herein.  
         BACKGROUND AND SUMMARY OF THE INVENTION  
         [0002]    The present invention relates to a belt tightener of a seat belt for an occupant on a seat in a vehicle, in particular a motor vehicle. The belt tightener has a retracting device, which is actuated by a retracting spring, for automatic shortening of the belt, and an extension lock of the belt, which lock is effective at predetermined parameters, in particular at a predetermined deceleration or acceleration of the vehicle or of its bodywork and/or when a predetermined extension speed of the belt is exceeded. An irreversible tensioning device is preferably provided. On obtaining an accident signal, which can be produced by a sensory mechanism, for example a signal for triggering an airbag, briefly, for example for 10 to 15 ms, the irreversible tensioning device brings about an irreversible tightening of the belt with great force, for example 4000 N.  
           [0003]    In a belt tightener of this type currently used as standard in motor vehicles, the retracting device is actuated by a spiral spring which has a structurally predetermined prestress when the belt is pulled in and, when the belt is extended, is increasingly stressed in accordance with its spring characteristic.  
           [0004]    The extension lock operates using mechanical catch elements. The latter are controlled, on the one hand, by inertial elements which are shifted from a catch-ineffective position into a catch-effective position if forces acting on the vehicle bodywork bring about a bodywork acceleration or deceleration exceeding a small threshold value. On the other hand, centrifugal elements are deflected from a catch-ineffective position into a catch-effective position if a reel, which is used for accommodating the belt, is rotated at a rotational acceleration exceeding a threshold value or jerkily in the extension direction of the belt. This ensures that the belt is securely locked against (further) extension of the belt in the case of danger-prone driving situations or even accidents.  
           [0005]    In view of the fact that the driver and/or—in particular—the front passenger of a vehicle can at least temporarily take up a position outside the normal or desired seat position, irreversible tensioning devices are assigned to the belt tighteners, at least in higher quality vehicles, which devices typically operate pyrotechnically and are triggered if a corresponding sensory mechanism “reports” a collision of the vehicle or triggers an airbag present in the vehicle. These irreversible belt tighteners are used for shortening the seat belt with great force. In this manner, any slack in the belt against the occupant&#39;s body and at or on the belt reel is eliminated and also, once a previously triggered airbag is relaxed, ensures optimum safety for the particular occupant in respect of possible secondary collisions. In each case, the occupant is kept as afar away as possible from hard structural parts of the vehicle bodywork.  
           [0006]    In order to improve the comfort, it is known, according to German publication DE 39 38 081 A1, to assign an electric motor to the spring provided for actuating the retracting device, in order to adjust the relatively stationary abutment of the retracting spring. In this manner, the belt tension can be changed and the effect can be achieved, in particular, that even with a greatly extended belt, as is necessary if the occupant is of above-average height or plumpness, the belt tension remains low and, accordingly, the wearing comfort is improved. As soon as the belt is withdrawn for winding-up purposes, the relatively stationary abutment is withdrawn into a starting position by the abovementioned motor, so that the belt can be wound up safely.  
           [0007]    Similar arrangements are the subject matter of German publications DE 41 12 620 A1, DE 195 01 076 A1 and of international publication WO 01/85495 A2. The last-mentioned publication reveals a belt tightener having a retracting spring, an electric motor which can be activated in a danger situation and a pyrotechnical tightening device.  
           [0008]    One object of the invention is to provide a belt tightener which is improved both in respect of comfort and in respect of safety.  
           [0009]    This object is achieved according to the invention in the case of a belt tightener of the type mentioned above by including a counterspring having a belt-remote abutment which can be adjusted by a motor arranged parallel to the retracting spring, and a normally open coupling arranged between the motor and the retracting device. The motor can be reversed between two power ranges, and the coupling closes automatically if the motor switches to high power and operates in its running direction provided to give reversible belt tightening.  
           [0010]    One general concept of the invention is that of driving the retracting device when the need arises, i.e. in the case of a danger situation determined by sensors, to give reversible tightening of the belt in such a manner that any belt slack which is present is completely withdrawn and the belt is effectively always tightened before an accident can arise from the danger situation. Danger situations can be recognized by sensor, for example, by the fact that the operating state of the vehicle brake and/or accelerations of the vehicle in the longitudinal and transverse direction are detected. A severe brake actuation and/or severe accelerations or decelerations of the vehicle point to hazardous situations.  
           [0011]    By means of the reversible belt tightening provided according to the invention, significantly increased safety can therefore be ensured. In particular, the irreversible tensioning device can act more rapidly, so that the occupant is retained at a very early point by the belt during an accident.  
           [0012]    On the other hand, the motor, which is provided for the reversible tightening of the belt, provides, by means of its connection or connectability in terms of drive to the belt-remote abutment of the counterspring, the possibility of ensuring particularly great comfort in normal driving situations by the motor adjusting the belt-remote abutment of the counterspring with the effect of reducing the effective tension of the retracting spring, so that the occupant virtually does not notice the belt. In the case of possible movements of the occupant, the belt-remote abutment of the counterspring can temporarily be released or can be adjusted with the effect of increasing the effective pull-back force of the retracting spring, in order to improve the belt retraction which may be necessary.  
           [0013]    In a similar manner the tension of the counterspring can also be reduced, and therefore the effective tension of the retracting spring increased, if the belt is released from the belt buckle or remains unused. The belt can thereby be rapidly shortened when not in use and can be kept in the non-use state by means of relatively strong spring force.  
           [0014]    The motor provided for adjusting the spring abutment of the counterspring therefore has multiple functions. Firstly, it can improve the wearing comfort of the belt and also facilitate the use of the belt. Secondly, the motor can immediately set a greatly increased belt tension in a danger situation in order to “prepare” the belt system for a possible accident.  
           [0015]    According to a preferred embodiment, the motor and/or its driving connection to the belt-remote abutment of the counterspring are designed to be self-locking, so that the set position of the spring abutment is maintained without supply of energy when the motor is at a standstill.  
           [0016]    According to a particularly preferred embodiment of the invention, a further coupling is arranged between the motor and the belt-remote abutment of the counterspring, which coupling closes if the motor runs counter to its running direction for the reversible belt tightening.  
           [0017]    The coupling, which closes in the case of the reversible belt tightening, is preferably designed as a gradient coupling which is only capable of closing given sufficient differences in speed between the coupling inlet and coupling outlet.  
           [0018]    If appropriate, the abovementioned coupling may also be designed as a centrifugal coupling.  
           [0019]    In an expedient refinement, a clamping-roller freewheeling device having a braked clamping-roller cage may be provided for this purpose.  
           [0020]    Otherwise, with regard to preferred features of the invention reference is made to the claims and the following explanation of the drawing which will be used to describe a particularly preferred embodiment of the invention in greater detail.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 shows a diagrammatic illustration of a belt tightener system according to the invention,  
         [0022]    [0022]FIG. 2 shows an axial section of the retracting device with retracting spring, counterspring and coupling arrangements, and  
         [0023]    [0023]FIG. 3 shows a partially cutaway axial view of the retracting device corresponding to the arrow III in FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    According to FIG. 1, a seat belt  1  has, in a known manner, a buckle latch  2  which is fastened to it and can be introduced in the customary manner into a belt buckle  3  and can be separated from the belt buckle  3 . The seat belt  1  is wound up on a reel in such a manner that the seat belt  1  has the respectively desired and required length. This will be explained in greater detail further below.  
         [0025]    The reel  4  is assigned, in a known manner, a mechanical extension lock  5  which locks the reel  4  against rotation in the unwinding direction of the seat belt  1  if the rotational speed of the reel  4  and/or the acceleration or deceleration of the vehicle, in which the seat belt  1  is arranged, exceed a threshold value.  
         [0026]    Furthermore, the reel  4  can be assigned an irreversible tensioning device  6  which operates in a known manner pyrotechnically and is ignited if a sensory mechanism on the vehicle recognizes a collision or an immediately imminent collision of the vehicle. In this case, the tensioning device  6  brings about irreversible belt tightening with very great force, for example 4000 N. The effect which can be achieved thereby is that the occupant secured by the seat belt  1  is protected to a particular extent against collisions with interior parts of the vehicle.  
         [0027]    In addition, the reel  4  is equipped with a retracting device  8  parallel to the extension lock  5 , in order to be able to wind up and shorten the seat belt  1  when not in use if the occupant has extended the belt on account of a movement of his/her body and moves back again into his/her desired seat position.  
         [0028]    The retracting device  8  has, for this purpose, a retracting spring  9  which is designed as a spiral spring, as will be illustrated further below, one end of the retracting spring  9  being connected fixedly to the reel  4  or to a shaft (not illustrated in FIG. 1) which is rotationally fixed with respect thereto, and the other end of the retracting spring  9  being connected fixedly to a stationary abutment.  
         [0029]    A counterspring  10  is arranged parallel to the retracting spring  9 , which counterspring can likewise be designed as a spiral spring, but with an opposite coil direction with respect to the retracting spring  9 , one end of the counterspring being connected fixedly to the reel  4  or to the shaft connected in a rotationally fixed manner thereto, while the other end of the counterspring  10  is connected fixedly to the outlet of a coupling  11 , the inlet of which is drive-connected to an electric motor  13  via a driving connection  12 , for example a toothed belt mechanism. The driving connection  12  and/or the electric motor are designed to be self-locking.  
         [0030]    Parallel to the coupling  11  and to the counterspring  10 , which is arranged in series therewith, a further coupling  14  is arranged between the driving connection  12  and the reel  4  or the shaft connected in a rotationally fixed manner thereto, which coupling closes automatically if the electric motor  13  is switched to a high power stage and rotates in accordance with the winding-up direction of the belt reel  4 .  
         [0031]    A control circuit  15  which is connected on the input side to a sensory mechanism for various operating parameters is used for controlling the power of the electric motor  13 .  
         [0032]    This sensory mechanism can have a sensor  16  on the buckle, the signal of which indicates whether the buckle latch  2  is inserted into the belt buckle  3  or not.  
         [0033]    Furthermore, a sensor arrangement  17  is provided which permits dangerous or danger-prone driving situations to be detected. For example, the sensor arrangement  17  can detect the actuation of the accelerator pedal and brake pedal, the response of a brake-assisting device and the fluid pressure in the brake system, and therefore the actuating state of the vehicle brake of the vehicle. In addition or as an alternative, the sensor arrangement  17  can also recognize and evaluate parameters dynamic for driving purposes, such as, for example, transverse acceleration, yaw rate, steering angle and/or vehicle decelerations.  
         [0034]    In addition, a rotary transmitter  18  or another sensor can be provided, the signals of which show whether the reel  4  of the seat belt  1  is being rotated or the seat belt  1  is being moved in the pull-in or extension direction.  
         [0035]    The control circuit  15  operates as follows:  
         [0036]    The initial starting point is that the sensor arrangement  17  does not report a dangerous state. In addition, the occupant may have put his seat belt on and may not have moved significantly for a relatively long time.  
         [0037]    The control circuit  15  can determine this state from the signals of the sensor  16  on the belt buckle  3  and of the sensor  18  on the reel  4 . The electric motor  13  is then activated in such a manner that it rotates in its direction of rotation for tensioning the counterspring  10 . In this direction of rotation the coupling  11  closes while the coupling  14  opens or remains open. The counterspring  10  is set to a more or less high tension in accordance with the rotational travel of the motor  13 . Since the tension of the counterspring  10  counteracts the tension of the retracting spring  9 , the abovementioned adjusting travel of the electric motor  13  has the consequence that the retracting force which is effective and can be sensed at the seat belt  1  is correspondingly reduced, for example to a low value of 2 N. In this manner, the wearing comfort of the belt  1  is quite substantially increased.  
         [0038]    If the occupant bends forwards at a moderate speed, the seat belt  1  is correspondingly extended. This movement of the belt  1  is reported by the rotary transmitter  18  of the belt reel  4  and can cause the control circuit  15  to drive the electric motor  13  at low power in such a manner that the tension of the counterspring  10  is reduced and, accordingly, the retracting force exerted on the belt reel  4  by the retracting spring  9  is increased in order to wind up the belt  1 . This ensures that the seat belt  1  readily follows the occupant if he/she moves back into his/her normal position from the position in which he/she is bent temporarily forwards.  
         [0039]    After a predetermined interval after the last belt movement reported by the rotary transmitter  18 , the motor  13  can then adjust the counterspring  10  again in such a manner that the belt tension is returned again to the very low value of, for example, 2 N.  
         [0040]    The belt  1  thereby loads the occupant with an extremely low force virtually continuously.  
         [0041]    If, during the journey, a dangerous or danger-prone driving state, for example a driving state with severe brake actuation, is reported by the sensor arrangement  17 , the control circuit  15  reverses the motor  13  to a high power range in the pull-back direction of the seat belt  1  and of its reel  4 , the normally open coupling  14  closing at the same time. The motor  13  therefore drives the reel  4  with great force, and the seat belt  1  is pulled tight with a correspondingly great force, for example 20 N or more. This reversible belt tightening ensures that the seat belt  1  bears tightly against the occupant&#39;s body and, in particular, any slack in the seat belt  1  which may be present or has been caused by the occupant is very rapidly withdrawn. Should an accident actually occur now, it is ensured that the occupant falls into a well-tightened seat belt  1 .  
         [0042]    If the belt latch  2  is released from the belt buckle  3 , the sensor  16  produces a corresponding signal. This can result in the control circuit  15  again activating the motor  13  in such a manner that the latter runs at low power in that direction of rotation in which the tension of the counterspring  10  is reduced and the coupling  11 , which has previously been closed if appropriate, is opened. In this manner, the spring tension of the retracting spring  9  is effective in an undiminished manner for retracting the seat belt  1 , i.e. the seat belt  1  is rapidly and completely wound up and retained in the wound-up non-use state by the retracting spring  9 .  
         [0043]    [0043]FIGS. 2 and 3 illustrate by way of example the manner in which the retracting device  8  can be designed together with retracting spring  9 , counterspring  10  and couplings  11  and  14 .  
         [0044]    The reel  4 , only part of which is illustrated in FIG. 2 and which is mounted rotationally on a frame  19 , is connected via a shaft  20 , which is connected in a rotationally fixed manner to it, to the radially inner end of the retracting spring  9  which is designed as a spiral spring and the radially outer end of which is secured in a stationary manner, i.e. fixed on the frame. Furthermore, the shaft  20  is connected to the radially inner end  10 ′ of the counterspring  10  which is likewise designed as a spiral spring and the coil direction of which is opposite to the coil direction of the retracting spring  9 . The radially outer end  10 ″ of the counterspring  10  is fastened to a spring abutment  21  which is mounted rotationally on the shaft  20 , is in the form of an internal geared wheel and is provided with an end toothing  21 ′ on its side facing away from the counterspring  10 .  
         [0045]    Axially between the spring abutment  21  and the retracting spring  9 , a sleeve part  22  is arranged in a rotationally fixed manner on the shaft  20 , the rotationally fixed connection being ensured by a strip  23  which protrudes radially out of the shaft  20  and engages in a corresponding axial groove on the inner circumference of the sleeve part  22 .  
         [0046]    The sleeve part  22  is mounted rotationally, by means of a subregion of its outer circumference, in a stationary sleeve  24  with the interconnection of a sliding ring. Mounted rotationally on the outer circumference of the stationary sleeve  24 , with the interconnection of a further sliding ring part, is a radially outer sleeve part  25  on whose outer circumference a gearwheel  27  is arranged rotatably and axially displaceably with the interconnection of a sliding sleeve  26 .  
         [0047]    This gearwheel  27  has an end toothing  27 ′ which, given an appropriate, axial displacement of the gearwheel  27 , engages in the end toothing  21 ′ of the spring abutment  21  with a rotationally fixed coupling of the gearwheel  27  and spring abutment  21 .  
         [0048]    The ring-shaped gearwheel  27  is passed through radially by a slot  28  which is orientated obliquely with respect to the circumferential direction and interacts in the manner of a slotted guide with a pin  29  which protrudes radially outwards out of the sleeve part  25  and is arranged in a stationary manner relative to the sleeve part  25 . If a torque thus occurs between the sleeve part  25  and the gearwheel  27 , the gearwheel  27  will rotate relative to the sleeve part  25 , in accordance with the size of the slot  28 , in the circumferential direction of the gearwheel  27 , in which case, depending on the direction of rotation, an axial displacement takes place to the right or left, in FIG. 2, the slot  28  being dimensioned in such a manner that the gearwheel  27  can engage with its end toothing  27 ′ in the end toothing  21 ′ of the spring abutment  21 .  
         [0049]    The axial end regions of the sleeve parts  22  and  25 , which regions are on the left in FIG. 2, form together with clamping rollers  30 , which are arranged radially between them, a clamping-roller freewheeling device, as will be explained below. The clamping rollers  30  are assigned a sleeve-like cage  31  whose one axial half has corresponding cutouts for receiving the clamping rollers  30  and whose other axial half can be rotated on the stationary sleeve  24  against braking resistance. The braking resistance is reduced by a friction ring  32  which is arranged in a circumferential groove of the stationary sleeve  24 .  
         [0050]    As can be gathered in particular from FIG. 3, that part of the sleeve part  22  which interacts with the clamping rollers  30  has a circular outer circumference while on that axial section of the inner circumference of the sleeve part  25  which interacts with the clamping rollers  30  clamping ramps  25 ′ are formed in such a manner that the clamping rollers  30  are inevitably clamped between the sleeve parts  22  and  25  when the sleeve part  25  rotates relative to the clamping-roller cage  31  and to the sleeve part  22  in the arrow direction A.  
         [0051]    The gearwheel  27  is, as is illustrated only in a diagrammatized manner in FIG. 1, drive-connected to the electric motor  13  via the driving connection  12 .  
         [0052]    If the gearwheel  27  in FIG. 3 is rotated in the arrow direction B, it is displaced axially to the left in FIG. 2, so that the end toothing  27 ′ of the gearwheel  27  enters into engagement with the end toothing  21 ′ of the spring abutment  21 . In addition, during the abovementioned rotation of the gearwheel  27  in the arrow direction B the sleeve part  25  is rotated at the same time via the pin  29 . As a result, therefore, firstly the gearwheel  27  is coupled to the spring abutment  21 , so that on further rotation in the direction B the counterspring  10  is increasingly tensioned. Secondly, the clamping rollers  30  take up their free-wheeling position between the sleeve parts  22  and  25 , i.e. the gearwheel  27  is uncoupled from the shaft  20 .  
         [0053]    On rotation of the gearwheel  27  in the arrow direction A, the gearwheel  27  is displaced axially to the right in FIG. 2, the end toothing  27 ′ of the gearwheel  27  emerging out of the end toothing of the spring abutment  21  and releasing the spring abutment  21 . The tension of the counterspring  10  can therefore be relaxed.  
         [0054]    If the gearwheel  27  is rotated further in the arrow direction A of FIG. 3, in particular at high power of the electric motor  13 , the sleeve part  25  is rotated at the same time in the arrow direction A as soon as the pin  29  strikes against the corresponding end of the slot  28 . This has the consequence that the clamping rollers  30  are clamped against the outer circumference of the sleeve part  22  by the clamping ramps  25 ′ and the sleeve parts  25  and  22  are accordingly coupled to each other. This then results, on further rotation of the gearwheel  27  in the arrow direction A, in the shaft  20 , which is connected in a rotationally fixed manner to the sleeve part  22 , being rotated at the same time in the arrow direction A and the coil  4  accordingly being rotated in the winding-up direction of the seat belt  1 . In this manner, the above-explained, reversible belt tightening is made possible.  
         [0055]    In a departure from the embodiment which is illustrated in the drawings, the irreversible tensioning device may, instead of being arranged on the coil  4 , also be arranged on the buckle  3  or on the end fitting (not illustrated) of the lap belt which continues the illustrated chest belt  1  at the belt latch  2 , the belt latch  2  being arranged in an easily displaceable manner on the belt.  
         [0056]    The arrangement on the reel  4  is advantageous in order to achieve particularly good tightening of the belt in the chest region.  
         [0057]    The arrangement on the end fitting brings about particularly good belt tightening in the lap region. An arrangement on the buckle makes possible a particularly good compromise with regard to tightening in the chest and lap region particularly in the case of a customary, combined chest and lap belt.  
         [0058]    The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.