Abstract:
A buckle pretensioner for a vehicle safety restraint comprising a buckle head ( 1 ) for receiving a buckle tongue to secure safety restraint webbing about a vehicle occupant in a three-point belt system; a cable ( 2 ) connected to the buckle head ( 1 ); and device ( 7 ) for rapidly withdrawing the cable in a belt tightening direction, the withdrawing device ( 7 ) comprising a force reservoir ( 8 ), and driving mechanism ( 6 ), and being of a compact construction through the use of set-up gearing ( 3,4 ) to magnify linear movement produced by the force reservoir ( 8 ) which may be a pyrotechnic gas generator or a spring. The driving mechanism ( 8 ) may be a piston-cylinder ( 6,8 ) or a rack and pinion. The gearing may comprise a pulley arrangement ( 3,4 ). Alternatively a roots motor or a gear pump could be used.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a buckle pretensioner for a vehicle safety restraint. 
     Pretensioners are used to rapidly withdraw a length of seat belt webbing in the event of an emergency. This takes up slack in the seat belt which might be caused by bulky clothing or by a vehicle occupant being out of position such as when leaning forward in the seat, or when seated skewed for example when asleep. The purpose of eliminating this slack is to more securely restrain the vehicle occupant at the onset of emergency conditions, and to more correctly position him for maximum effect of any secondary safety restraint such as an airbag. 
     Pretensioners may be situated at the retractor end of a three-point safety belt to rapidly rewind the belt webbing, or alternatively at the buckle end to rapidly pull back the buckle mounting. 
     Known buckle pretensioners use a piston-cylinder arrangement in which a piston connected to the buckle mounting is pushed rapidly along a cylinder by the force of a spring or more recently by pyrotechnic means which release a sudden rush of gas. Such arrangements are bulky and difficult to fit unobtrusively in a vehicle, particularly in the smaller models of vehicle which are popular nowadays. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved buckle pretensioner and particularly a more compact design. 
     According to the present invention there is provided a buckle pretensioner for a vehicle safety restraint comprising a buckle head for receiving a buckle tongue to secure safety restraint webbing about a vehicle occupant in a three-point belt system, the pretensioner comprising; a cable connected to the buckle head and means for rapidly withdrawing the cable in a belt tightening direction, the withdrawing means comprising a force generator or reservoir and driving means and being more compact than hitherto known. 
     According to a first embodiment of the invention the pretensioner further comprises step-up gearing means for converting a linear movement of a predetermined magnitude, produced by the force generator, into a linear movement of the cable of more than the predetermined magnitude, preferably a multiple of the predetermined magnitude. 
     Gearing arrangements were not previously considered viable for pretensioners, particularly buckle mounted pretensioners because they increase the torque which must be generated by the driving means, the maximum torque from traditional driving means was limited. However the improvements in pyrotechnic force generators means that sufficient torque can now be generated rapidly enough. 
     The step-up gearing may comprise a multiple pulley arrangement, such that the withdrawal means operates on a small diameter pulley fixedly connected to rotate with a large diameter pulley about which the cable is wound. 
     This arrangement allows a relatively simple force reservoir to be used in the pretensioner because the necessary locking devices can be included in the pulley arrangement, for example a simple ratchet and stop, rather than being part of the force generator (for example in the tube of a piston-cylinder pretensioner) as hitherto. 
     This embodiment can also be adapted relatively easily to incorporate load limiting features. 
     It is particularly applicable to the use of a piston-cylinder type pretensioner, either with a spring or a pyrotechnic force generator and the cylinder tube can in this case be made much shorter than in previous pretensioners. 
     However this embodiment is equally applicable to other types of force generator or to other driving means. 
     According to a second embodiment the driving means comprises a rack and pinion arrangement. The rack may be vertical or horizontal and is driven past the pinion wheel which is connected to rotate a pulley about which the cable is wound, by spring force or by a gas generator. 
     The pinion wheel may be driven by more than one rack, as for example in a system with two moving racks one on either side of the pinion wheel in opposite directions to reinforce each other&#39;s driving force. Their movement may be synchronised or phased depending on the pretensioning characteristics to be achieved. 
     Force generators such as gas generator may be integral with the racks. 
     Gearing arrangements may advantageously also be incorporated in this embodiment. 
     According to a third embodiment, the driving means comprises at least two pulley wheels across which the cable passes and means for extending the distance between the pulley wheels so as to withdraw the cable in the belt tightening direction. 
     Two pulley wheels may be arranged adjacent the path of the cable and driven in opposite directions across the path of the cable so as to withdraw the buckle head. 
     Alternatively two or preferably more pulley wheels are arranged with the buckle cable wound around them in an S configuration and one or more pulley wheels are driven parallel to the cable to withdraw the buckle head. 
     A further alternative is to use an elongate, elliptical or oval, cam pulley, arranged in normal use with the cable passing along both its long sides and round one of its short sides. Under pretensioning conditions this cam pulley is rotated rapidly through approximately 90° so that its long sides are tangential to the path of the cable from the buckle head, thus quickly and easily shortening the effective length of cable from the buckle head to its mounting position. The cam pulley may be driven by a pyrotechnically detonated gas generator or by a spring, or by other force generator means. 
     A gas generator driven cam faced piston may be used instead. The buckle cable passes over the outer arcuate cam face of the piston. When pretensioning is required the gas generator drives the piston a predetermined distance away from the buckle head and thus shortens the effective length of the cable to the buckle head. 
     According to a fourth embodiment of the invention the driving means comprises a rotating part with paddles or vanes driven by gas from a gas generator. This may be a wheel connected to the cable pulley, with or without gearing, or a helix coaxial with the cable pulley. 
     Alternatively a Roots motor or gear pump could be used comprising two camming figure-of-8 drive parts, one driven by a gas generator, the other coaxial with the cable pulley. 
     For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made to the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a compact buckle pretensioner according to one embodiment of the invention. 
     FIG. 2 is an exploded view of a buckle pretensioner according to a variant of the embodiment of Figure 
     FIGS. 3 and 4 are exploded views of a second embodiment of the present invention. 
     FIG. 5 is an exploded view of the buckle pretensioner according to a variation of the second embodiment of the present invention. 
     FIG. 6 is a schematic cross-sectional view of a buckle pretensioner according to a third embodiment of the present invention. 
     FIG. 7 is a part cut-away view of a buckle pretensioner according to a variant of the third embodiment. 
     FIG. 8 is an exploded view of a buckle pretensioner according to another variant of the third embodiment. 
     FIG. 9 illustrates another variant of a buckle pretensioner according to the third embodiment. 
     FIG. 10 is an exploded, and part cut-away view of a buckle pretensioner according to a fourth embodiment of the invention. 
     FIGS. 11,  12 ,  13  and  14  show alternative variants of the fourth embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1 there is shown a buckle head  1  connected by a cable  2  to the outer diameter of a large diameter pulley wheel  3  Normally the cable would be covered with a plastic sheath and the buckle head is supported to be upstanding by a relatively stiff stalk but these are not shown in FIG.  1 . The pulley wheel  3  is attached to a smaller diameter pulley wheel  4  and the outer diameter of this is connected by cable  5  to piston  6  of pretensioner  7 . Piston  6  is arranged for sliding movement in the cylinder  8  and a gas generator  9  is arranged to be electrically detonated in the event of a crash being detected by crash sensors to release gas into the cylinder  8  to push piston  6  in the direction of arrow A. This has the advantage over traditional arrangements of providing a step up gearing of a ratio corresponding to the ratios of the circumferences of the two pulley wheels  3  and  4 . Thus movement of the piston a predetermined length along the cylinder  8  will move the buckle head downwards by a larger length depending upon the gearing ratio. Thus a more compact linear pretensioner can be used. 
     FIG. 2 illustrates a load limiting arrangement in a compact buckle pretensioner. The buckle cable  2  passes from the buckle (not shown) around pulley wheel  10 . One side of the wheel  10  is provided with sloping teeth which face correspondingly shaped sloping teeth  12  on the side of a locking ratchet  13  which has locking teeth  14  on its outer circumference. The locking teeth  14  can be engaged by locking pawl  15  which is rotatably mounted on the casing of a buckle pretensioner  16 . The locking ratchet  13  and pulley wheel  10  are mounted on and coaxial with drive shaft  17  of the compact pretensioner  16 . They are fixed on the drive shaft  17  by a bolt or rivet  18  and a spring clutch arrangement  19  is mounted between the rivet  18  and the pulley wheel  10 . The pretensioner  16  is fired by electrically detonated gas generator  9 . However, other firing means may be used. 
     Spring  19  acts on pulley wheel  10  to keep it engaged, via the interlocking sloping teeth  11  and  12 , with the locking ratchet  13  up to a predetermined torque. Above the predetermined torque the sloping teeth  11  and  12  slip over each other and allow the pulley wheel  10  to rotate independently of the locking ratchet  13 . Thus a maximum load is applied to the vehicle occupant restrained by this buckle. 
     FIG. 3 shows an alternative compact buckle pretensioner. The buckle head (not shown) is again connected via cable  2  to a pulley wheel  10 . One section of the pulley wheel  10  has teeth  20  about its outer circumference. These teeth are engaged by corresponding teeth  21  on a horizontal rack  22  which is driven tangential to the pulley wheel  10  by electrically detonated gas generator  9 . The pulley wheel  10  is protected by an outer cover  23  and is mounted for rotation and secured in place by rivet or bolt  18 . 
     FIG. 4 shows an alternative arrangement to FIG. 3 in which the rack  22  is vertically mounted. Otherwise like parts are denoted by like reference numbers. In FIGS. 3 and 4 a seal  24  is situated between the rack  22  and pretensioner housing wall  25 . This maximises the effect of the gas generator by preventing escape of gas along the side of the rack. In addition a locking means is provided so as to lock the rack and pinion in the pretensioned state after pretensioning to hold the buckle in the retracted position. This may, for example be, in the form of a locking ellipse as is well known in this field and as is shown in GB 1 351 447 and also is described in DE 42 34 132 both of which are incorporated herein by reference. 
     FIG. 5 shows an alternative compact buckle pretensioner. Again buckle cable  2  is connected to a pulley wheel  10  mounted on shaft  26 . A tooth pinion wheel  27  is mounted on shaft  26 . Two sets of tooth racks are arranged one on either side of the pinion wheel  27  so that when activated they move across the pinion wheel engaging the teeth and rotating it. Single or multiple racks  28  and  29  are mounted on respective support blocks  30 ,  31  and the parts are contained within housing parts  32 ,  33 . An electrically detonated gas generator  9  acts to push the support blocks  30 ,  31  with their respective racks  28 ,  29  along the respective channels formed by the two parts of the covers  32 ,  33 . The gas from the gas generator  9  pushes support members  30  and  31  by acting on planer surfaces of the support end members  34 ,  35 . 
     FIG. 6 illustrates another embodiment of the invention. In FIG. 6 a  the buckle is shown in the normal use condition. In FIG. 6 b  the pretensioner has operated and the buckle head  2  has been retracted. This is effected by driving two rods  36  and  37  in opposite directions across the path of the cable  2  as indicated by the arrows. 
     FIG. 7 shows a similar arrangement in which multiple pulleys are introduced and the rods are pushed in a direction parallel to the buckle cable  2 . This arrangement is even more compact than that of FIGS. 6 a  and  6   b . FIG. 7 a  is a schematic diagram showing buckle head  1  attached via cable  2  to split cables  38 ,  39  which pass over respective pulley wheels  40 ,  41  and are fixed at points  42 ,  43  to the pretensioner housing  44 . A drive arrangement  45  comprises two pusher fingers  46  and  47  which act on respective split cables  38 ,  39 . An electrically detonated gas generator  9  or other drive means acts on the outer planer face of the pusher member  45  to drive it in the direction of the arrow thus pulling in a predetermined length of buckle cable  2  to retract the buckle head  1 . This same arrangement is shown in FIG. 7 b  in part cut-away cross-sectional view where like references denote like parts. 
     FIG. 8 shows a similar arrangement in which the buckle cable  2  passes around an elliptic cam  48 . The pretensioner drive means, such as electrically detonated gas generator  9 , rotates this cam  48  in the direction of the arrow so as to take up a predetermined length of cable  2  and thus retract the buckle head. 
     FIG. 9 uses a pusher member  49 , driven by gas generator  9  to take up a length of cable  2 . 
     FIG. 10 shows an embodiment which uses a vane motor  50  as a pretensioning drive force. The vane motor  50  is contained within a housing  51  and is driven by electrically detonated gas generator  9 . An exhaust port  52  is provided in the housing  51 . The vane motor  50  is mounted for rotation via the fixing screw  18  which also passes through the motor drum casing  53  and a cable pulley wheel or winch drum  10  about which the buckle cable  2  passes. 
     FIG. 11 shows a variation of this vane motor which has a single paddle  54  instead of multiple paddles as in FIG.  10 . 
     In FIG. 12 another variation is shown using a tri-lobe motor  55  in housing  51 . Again this is driven by electrically detonated gas generator  9 , though the person skilled in the art will see that there are many satisfactory alternative drive means. 
     FIG. 13 shows a screw driven buckle pretensioner in which a helical drive shaft  56  is rotated by the force from electrically detonated gas generator  9 . Seals  24  assist the gas generator  9  in operating efficiently. Preferably the pulley wheel on winch drum  10  has reverse locking to prevent it from rotating in a cable loosening direction. 
     FIG. 14 is an embodiment using a rotor drive or a Roots motor. This comprises two figure-of-8 rotors  57 ,  58 . The drive rotor  57  is mounted for rotation about fixing screw  18  which also fixes the winch drum  10  about which buckle cable  2  is wound. The idler rotor  58  is driven by gas generator  9  and this drives the drive rotor  57  and consequently winch drum  10  to pull back the buckle cable  2  and thus the buckle head (not shown). 
     It will be seen in all these examples that the buckle pretensioner is particularly compact and suitable for siting in convenient and unobtrusive positions in a vehicle close to the buckle head, or at a distance as required by the vehicle manufacturer.