Patent Publication Number: US-6213513-B1

Title: Buckle pretensioner

Description:
This is a continuation, of prior application No. PCT/US98/24515, filed Nov. 16, 1998 , which designated the United States of America which is in turn a Continuation-in-part of prior U.S. application Ser. No. 08/970,849, filed Nov. 14, 1997 now 5,944,350 which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a pretensioner for safety belt systems securable to a vehicle chassis and more particularly to a pretensioner having a power-operated device for drawing a flexible member to remove slack from the seat belt system. 
     BACKGROUND OF THE INVENTION 
     A pretensioner for a seat belt system is disclosed in U.S. Pat. No. 5,588,677, which is assigned to the assignee of this invention, and in this pretensioner a buckle part of a three point seat belt system is connected to a flexible draw element in the form of an elongated wire cable. The wire cable has a loop portion looped about a roller secured to the buckle part. One end of the loop portion is secured and the other portion of the loop is pulled downwardly by a power-operated device. The preferred power-operated device has a piston which travels horizontally and pulls the attached horizontal cable portion horizontally which in turn pulls down the other portion of the loop and the attached buckle part. The loop splits the force being applied to the buckle in half, e.g., about 2,600 lbs. on each half of the loop but the loop requires twice the travel distances for the cable for each increment of downward buckle travel. 
     Typically, the power-operated device is a pyrotechnic gas generator that drives a piston to travel the distance necessary to remove the slack from the seat belt system. Such cylinders are usually located on or about the seat. In some instances, there is a lack of sufficient space for such a long cylinder, and there is a desire to provide a more compact pretensioner of this kind. 
     When the piston has traveled the full extent of the cylinder and has taken out the slack, the pretensioner will have pulled the person down into the seat, and thereafter the person and attached seat belt system begin to rebound upwardly. To prevent the passenger from rebounding and returning slack into seat belt system, a one-way locking mechanism becomes effective to resist the rebound travel of the cable. Such an automatic locking of the return travel of the wire cable is disclosed in German published application DE 42 30 663 published Mar. 17, 1994. 
     The pulling force of the pretensioner on the buckle part is quite large, and where the buckle part is a buckle having a locking mechanism operated by a push button, it is preferred to have a latch or blocking member that is shifted to a blocking position to prevent the push button from traveling to release the latch plate. European published patent application 0 557 073, published Jun. 29, 1993, discloses a pivotally mounted blocking member that is biased by a spring to a normal, non-blocking position and that is pivoted against the spring bias by the gas generator to a blocking position. In the blocking position, the blocking member engages and blocks travel of the push button member in the release direction. Thus, the gas generator causes a blocking of the buckle release at the time that the pretensioner is removing slack from the seat belt system. 
     When the acceleration sensor activates the pretensioner, it activates both the driver&#39;s pretensioner as well as the passenger&#39;s pretensioner. If the driver or the passenger is not wearing the seat belt system at the time of actuation of the pretensioner, the buckle travels downwardly very rapidly and hits its buckle housing so hard against the pretensioner housing that the buckle housing can crack or break. In order to avoid a liability claim, where a person not wearing the seat belt system alleges to have been wearing it and alleges that the seat belt buckle failed as evidenced by the broken buckle housing, it would be desirable to provide an energy absorption device or member to absorb energy and dampen the buckle impact such that the buckle housing doesn&#39;t break. Thus, a potential liability claim could be avoided. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a shortened piston stroke is used and achieves the necessary displacement of a buckle portion and an attached seat belt to remove slack from the seat belt system. This is accomplished by forming a loop of cable inside of the cylinder with the loop being connected to the piston. Preferably, the cable loop about the buckle and the cable about the piston are equal so that they have about a 1:1 ratio. Thus, for each unit of travel of the piston, there is an accompanying unit of travel of the buckle part. Herein, the cable is looped about a turning member within the piston with one end of an anchored half of the cable loop secured to a stationary part of the pretensioner; and the other extendible half of the loop extending from the cylinder connected to the cable portion for the buckle part. 
     Preferably, an energy absorber is provided with the pretensioner. The energy absorber is impacted by the buckle as it is accelerated by the power-operated device; and the energy absorber limits damage to the buckle part as it is pulled toward the pretensioner. The preferred energy absorber is in the form of inexpensive, plastic tubes located about the wire cable loop portions connected to the seat belt buckle. The buckle part deforms and deflects the tubes, thereby dissipating energy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in the following by way of example and with reference to the drawings wherein: 
     FIG. 1 is an exploded view of a pretensioner embodying the preferred embodiment of the invention; 
     FIG. 2 is an enlarged view of a piston and stationary plate with the cable looped about a pin in the piston; 
     FIG. 3 is an enlarged cross-section of the pretensioner of FIG. 1; 
     FIG. 4 is a schematic partly sectioned side view of a belt tensioner of the invention which is mounted on a vehicle chassis; 
     FIG. 5 is a schematic sectional view on the line 5—5 in FIG. 5; 
     FIG. 6 is a plan view of the pretensioner of FIG. 7; 
     FIG. 7 is a side elevational view of the pretensioner of FIG. 6; 
     FIG. 8 is a cross-sectional view similar to FIG. 3 showing the looping of the cable about a pulley member rotatively mounted to the piston; 
     FIG. 9 is an exploded perspective view of the pulley member and piston; 
     FIG. 10 is a side elevational view of the piston of FIG. 9; 
     FIG. 11 is an end elevational view of the piston of FIG. 9; 
     FIG. 12 is a cross-sectional view taken along line 12—12 of FIG. 11; 
     FIG. 13 is a cross-sectional view taken along line 13—13 of FIG. 11; 
     FIG. 14 is an elevational view of the pulley member of FIG. 9; and 
     FIG. 15 is a cross-sectional view taken along line 15—15 of FIG.  14 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in the drawings for purposes of illustration, the invention is embodied in a pretensioner  50  having a flexible member such as a wire cable  13  connected to a buckle part which could be either a latch plate (not shown) or the illustrated buckle  15  having a push button  15   a  and a housing  15   b.  The wire cable  13  is connected to a power-operated device  11  which is connected to and operable by an acceleration sensor  52  (FIG.  7 ). The power-operated device may take various forms and be operable by springs, compressed gas or the illustrated and preferred power-operated device is pyrotechnically operated and comprises a piston and cylinder unit  51  by electrical signals over electrical leads or wires  53  from the acceleration sensor  52 . The illustrated power-operated device  11  comprises a piston  25  slidable in a cylinder  26  (FIG.  3 ). The rear cylinder space  27  of the piston and cylinder unit  51  at the end remote from the piston  25  has an opening  28  leading to the atmosphere while the cylinder space  29  located in front of the piston  25  is connected to a pyrotechnical pressure generating device  30  which can be connected by the wires  53  to the illustrated acceleration sensor  52 . In the event of an accident, the sensor  52  causes a triggering of the charge  32  located in the pyrotechnical pressure generating device  30  and a high pressure gas abruptly builds up in the cylinder space  29  which displaces the piston  25  rearwardly in the direction of the arrow F (FIG.  3 ). 
     The wire cable  13  is fixedly connected to the center of a piston  25  and passes through a sealed bore at the front end of the cylinder  26  and is then guided through a straight channel  34 . In the region of the straight channel a pull-back blocking device  35  is arranged around the wire cable  13 . 
     Referring now to the other end of the cable  13  and to FIG. 4, the wire cable  13  has a first end  55  secured by a fastening head or ferrule  24  (FIG. 4) to an abutment collar  39  on the pretensioner housing. The cable extends form this fixed first end  55  about a turning or deflection member  14  upwardly to an about a deflection roller  23  fixed to the buckle  15 . The cable is looped about the deflection roller  23  to form a first buckle loop  56  having loop portions  56   a  and  56   b,  which are looped about the buckle part. The loop portion  56   b  extends down to the deflection roller  14 . This buckle loop  56  is shortened when the piston  25  pulls the attached cable and travels to the right, as seen in FIGS. 4 and 5, with the loop portion  13   b  traveling down and the loop portion  13   a  also being shortened as the deflection roller  23  travels downwardly. Thus, it will be seen that it takes a relatively long cylinder to obtain the desired downward travel distance to remove the slack in the system disclosed in U.S. Pat. No. 5,588,677. 
     In accordance with the present invention, the length of the piston travel and of the cylinder  26  may be reduced very substantially, e.g., to provide about a 1:1 ratio between the length of piston travel and downward travel distance of the buckle  15 . This is achieved by forming a second or piston loop  58  in the cable  13  and having the power-operated device elongate the piston loop  58  as it shortens the buckle loop  56 . In the illustrated embodiment of the invention, the piston loop is formed with an anchored leg or loop portion  58   a  and an extendible leg or loop portion  58   b  (FIG.  3 ). Herein, the anchored loop portion  58   a  is anchored to a perforated member  60  by an enlarged fastening head or ferrule  62 . 
     The piston loop  58  is preferably formed about a turning member, such as a cylindrical pin  64 , which is mounted in a hollow chamber or portion  66  in the piston  25 . As the piston travels to left in FIG. 3, it draws the cable  13  further into the cylinder with the cable entering and lengthening the legs  58   a  and  58   b;  and these legs keep extending in length as the piston travels in the cylinder. When the piston has traveled the full length of the cylinder&#39;s bore, the pin will have greatly elongate the piston loop  58  while pulling down and shortening the buckle loop  56  in about a 1:1 ratio. 
     Referring now to FIGS. 2 and 3, the piston  25  has a head portion with an O-ring seal  76  which seals with the interior bore wall of the cylinder to prevent the gas from flowing about and past the piston head portion. 
     The stationary perforated member  60  has several perforations  67  to allow the expanding gas to flow into the hollow interior chamber  66  of the piston. The ferrule  62  abuts the plate at an elongate slot  68  through which the cable end extends. The perforated plate  60  is a disc of metal having a peripheral edge to seat against an annular shoulder  73  at the end of a threaded bore  70  in the pretensioner housing. A thread  75  on the end of the cylinder is threaded into the threaded bore, and an end wall  72  abuts stationary disc  60  to fix it in place. 
     Also, within the pretensioner housing is the one-way locking device that prevents the tension on the cable  13  being exerted during rebound of the occupant from pulling the piston  25  back and allowing slack to return with elongation of the buckle loop  56 . As disclosed in the German published application DE 42 30 663, published Mar. 17, 1994, a cable gripper  80  has a slotted portion with interleaved lugs  82  and a conically-shaped forward end  84  that can be cammed downwardly by a sloped conical wall  86  of the housing chamber. The space  88  can be collapsed in the upper portion of the forward end  84  as the cable gripper is being cammed to more tightly grip the cable  13  passing through the cable gripper. The cable slides freely through the cable gripper when the piston is being driven by expanding gas. However, during rebound of the occupant and a pulling of the cable  13  in the opposite direction, a knurled rotatable pin  92  will be rolled by cable up a ramp  94  in the cable gripper and wedged between the cable and ramp. When the pin  92  is wedged, the cable tension and rebound travel of the cable  13  will act through the wedged pin and ramp  94  to pull the cable gripper deeper into the socket where the inclined wall  86  causes the interleaved portion to be wedged down to grip tightly the cable  13 , thereby stopping further travel of the cable gripper and the cable  13  in the rebound direction. The knurled pin  92  is biased by a spring  98  to engage the cable. When the piston is traveling by the expanding gas, the knurled pin is shifted by the cable to further compress the spring  98  and to move the knurled pin away from the inclined ramp  94 . On the other hand, the cable, when traveling in the rebound direction, is assisted by the spring  98  to travel up the ramp  94  to wedge between the cable and the ramp  94 . A small spring retainer  99  retains the spring  98  in the proper position. 
     Referring in greater detail to the cable travel, it travels about the deflection member  14 , which has a deflection section  14 ″ of larger diameter and at the top a head guide section  14 ″″ having an even larger diameter. 
     A plate-like projection  20  extends from the front end of the drive device  11  in unitary manner up to and beyond the deflection member  14 . It is rounded off at the top at  37  and undergoes a transition there into an angled portion  21  which points obliquely upwardly and which can likewise be of plate-like design. 
     As can be seen in particular from FIG. 5, the projection  20  that a throughbore  19  of somewhat larger diameter in the region of a threaded bore  18  provided in the vehicle chassis  12  and a threaded bolt section  14 ′ of the deflection member  14  is screwed into the threaded bore  18  through the bore  19 . In doing so the horizontal ring step  14 ″″ located between the bolt portion  14 ′ and the deflection portion  14 ″ contacts the surface of the projection  20  around the throughbore  19  and thus presses the projection  20  against the vehicle chassis  12  so that the projection  20  including the drive device  11  and the angled portion  21  which are formed in one piece with it are securely fastened to the vehicle chassis  12 . In place of the bolt section  14 - a downwardly open sleeve section provided with an internal thread could also be provided which is screwed onto a threaded bolt which is secured to the chassis  12 ; for example, by welding, whereby the projection  20  can likewise be pressed against the chassis  12 . 
     Referencing FIGS. 8-15, an alternative piston assembly  100  will next be described. As the construction of cylinder  26  and the remainder of the pretensioner  50  remains substantially the same as that previously-described, it will not be discussed to any great detail further herein. As discussed with respect to piston  25  in FIGS. 2-5, the cable piston loop  58  wraps about a pin  64  transversely mounted in the piston chamber  66  for pulling of the cable  13  when the pretensioner fires and the piston  25  is driven for sliding in the cylinder  26 . Because pretensioner firing exerts such heavy loading and forces on the piston, substantial frictional rubbing and wear occurs at the interface between the cable  13  and pin  64  which is fixed to the piston  25  as the piston is driven and the cable  13  travels therearound. 
     Accordingly, the alternative piston assembly  100  incorporates a rotatable bearing in the form of pulley member  102  about which the cable loop  58  is wrapped. Thus, as the piston  104  is propelled in the cylinder  26 , the cable  13  will be pulled by the pulley member  102  which will rotate as the cable  13  travels around the pulley member  102  with the cable portions  58   a  and  58   b  lengthening. The rotation of the pulley member  102  lowers the friction generated on the cable  13 , and in particular between the cable  13  and the member  102  over that created with a fixed pin  64  when the piston is driven. The lowered friction in turn reduces the abrasion and wear on the cable  13  lessening the chance of its premature failure. 
     Turning to FIGS. 9-15 for a more detailed description of the alternative piston assembly  100 , the piston  104  has a solid head end  106  provided with an annular groove  108  for receipt of a seal in the form of a resilient O-ring seal member  110  therein which slides along the inside of cylinder wall  26 . The seal  110  keeps the expanding gas from passing past the piston head  106  when the pretensioner is fired. 
     At its opposite end, the piston  104  has an elongate slot  112  that opens to end face  114  of the piston  104  and extends diametrically thereacross opening along annular surface  116  of the piston  104 . The slot  112  as shown extends past the midpoint along the length of the piston  104  and ends at curved wall portion  118  with the slot  112  bounded on either side by parallel side wall portions  120  and  122 . 
     The side walls  120  and  122  are spaced so as to accept the pulley member  102  therebetween with slight clearance on either side of the pulley member  102  to allow for its rotation in the slot  112  when the pretensioner is fired. The piston also includes a transverse bore  124  that opens to surface  116  at points spaced approximately ninety degrees from where the slot  112  opens to the piston surface  116 . The bore  124  also opens to the slot sidewalls  120  and  122  in the piston slot  112  such that pin  126  tightly received in the bore  124  has a central portion  126   a  thereof exposed in the slot  112 . 
     The pulley member  102  has an annular shape including a central opening  128  for receipt of the pin  126  therethrough. The opening  128  is sized sufficiently large relative to the diameter of the pin  126  so that the pulley member  102  can rotate thereon. To provide for receipt of the loop  58  therearound, the exterior peripheral surface  130  of the pulley member  102  is recessed by way of a generally concave depression  132  to provide for greater surface contact with the cable  13  run therein. Finally, the diameter of the pulley member  102  is smaller than the diameter of the piston  104 , and is sized so that with the cable loop  58  wrapped therearound, the cable  13  will not project beyond the surface  116  of the piston  104 . 
     From the foregoing, it will be seen that the present invention provides an energy absorber to prevent breakage of a buckle part during a pretensioning operation. Further, the stroke of the piston and length of the cylinder may be reduced to provide a smaller and more compact pretensioner.