Abstract:
A pretensioner  10  for a seat belt  12  employs a strap  30  fixed about a pulley  34  and also fixed at an opposite end  36  to a housing  18.  Upon pretensioner activation, an actuator  20  is propelled across a rectangular passage  72  thereby impelling a portion  31  of the strap  30  extending across the passage  72.  Torque created by the strap  30  about the pulley  34  effects rotary advancement of the geared pulley  34  with a geared clutch  37  engaged therewith. The geared clutch  37  co-axially and rotatably communicates with a seat belt retractor spool  46  wherein a seat belt retractor spool shaft  40  axially extends through the clutch  37  and spool  46.  Activation of the pretensioner  10  therefore results in ignition of a gas generant  16  that produces sufficient gas pressure to drive the actuator  20  through a linear passage  72,  thereby effecting rotary movement of the pulley  34,  the clutch  37,  the shaft  40,  and the spool  46.  A seat belt  12  wound about the spool  46  is thereby pretensioned.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application Serial No. 60/209,376 filed on Jun. 5, 2000. This application is also a continuation in part of co-pending U.S. application Ser. No. 09/777,388 filed on Feb. 5, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to seat belt pretensioners and, more specifically, to a seat belt pretensioner that incorporates a plurality of simplified motion multipliers thereby reducing the actuator stroke requirement.  
           [0003]    Seat belt pretensioners remove slack from a seat belt in the event of a collision in order to minimize forward movement of the passenger. While it is known to use pyrotechnic gas generators to operate mechanisms which wind up or otherwise pull in slack of the seat belt during a collision, such known pyrotechnic gas generators are generally disposed internally of a seat belt retractor. Thus, the vehicle owner is faced with a significant cost penalty in that the entire pretensioner and retractor assembly must be replaced after activation because of the inability to prevent degradation of the retractor. High-temperature gases tend to abrade interior metal surfaces and produce ash and clinkers that bind up the retraction mechanism.  
           [0004]    Another problem with known pretensioners is that they are designed to activate only in severe accidents, for example, accidents that exhibit “G” forces sufficient to activate the vehicle airbags. Safety system designers generally choose such a relatively high activation threshold due to the expense of replacing the entire seat belt retractor and pretensioner assembly after activation. As a result, seat belt pretensioners do not protect passengers in less severe accidents.  
           [0005]    A related problem with known pretensioners is that when the pretensioner is activated only in severe accidents, activation is relatively late in the crash sequence. Thus, the pretensioner must rapidly take up slack in the seat belt, sometimes injuring the passenger.  
           [0006]    U.S. Pat. No. 5,967,440, herein incorporated by reference, describes a pretensioner and a conventional retractor for a safety belt system. When compared to the seatbelt retractor, the pretensioner is relatively complex and large, thus increasing the weight and spatial requirements of the seatbelt assembly.  
           [0007]    U.S. Pat. No. 5,899,399, herein incorporated by reference, describes a state of the art pretensioner. The pretensioner is relatively complex and as such complicates the manufacturing process.  
           [0008]    U.S. Pat. No. 5,944,350, herein incorporated by reference, describes a state of the art pretensioner. Again, the pretensioner is relatively large, thus increasing the weight and spatial requirements of the seatbelt assembly.  
           [0009]    German Patent No. DE 10010379 A1, herein incorporated by reference, describes a pretensioner having an arcuate path for a multi-piece actuator (a plurality of cylinders) that drives a steel cord wrapped around a webbing reel hub and thereby effects pretensioning of an associated seat belt. The manufacturing of the pretensioner is more complex given the multi-piece actuator and given the arcuate channel that the actuator must traverse. Uniformity in channel width and effective sealing becomes more difficult with the use of an arcuate channel. Secondly, a noise reduction means is employed to prevent rattling during normal vehicle operation, thereby increasing manufacturing costs. Furthermore, the joint use of the multi-piece actuator with the steel cord results in a friction loss and a reduction in the load applied to the steel cord by the forward-most cylinder of the actuator. As a result, more force is required to drive the multi-piece actuator and pretension the seatbelt. One solution is described by the use of an intermediate element “43” for facilitating the smooth movement of the rotating elements along the arcuate channel. Consequently, without the use of the intermediate element “43”, a more robust pretensioner housing would be necessitated to withstand the relatively greater combustion pressure (produced by a greater amount of propellant) likely necessary to pretension the seatbelt in accordance with customer requirements.  
           [0010]    Other pretensioner designs employ relatively complicated clutch assemblies for clutching a seat belt retractor axle associated therewith. Many known pretensioner drive systems are also relatively complex. U.S. Pat. Nos. 6,042,041, 5,842,344, 5,794,876, and 5,699,976, herein incorporated by reference, illustrate the complexity of known pretensioners. Simplification of known designs, therefore, is desirable given a resultant simplification of manufacturing requirements.  
         SUMMARY OF THE INVENTION  
         [0011]    The aforesaid problems are solved, in accordance with a preferred constructed embodiment of the present invention, by a seat belt pretensioner that utilizes a plurality of motion multipliers within an essentially sealed housing thereby preventing retractor exposure to combustion gases and clinkers. More specifically, the present invention utilizes a drive gear that is meshed or engaged with a geared clutch sleeve. A pair of clutch segments is fixed radially inward of the clutch sleeve and radially outward of a webbing reel shaft of a seat belt retractor for gripping the shaft upon pretensioner activation. The webbing reel shaft axially extends through the circumferentially opposed clutch segments and rotates freely during normal operation of the vehicle. The webbing reel shaft also extends through the house and axially through a webbing reel of the seat belt retractor thereby establishing coaxial communication between the activated clutch and the webbing reel. Inclusion of the clutch (clutch sleeve and clutch segments) within the pretensioner eliminates the need for a clutch operable within the retractor. The present design also prevents occupant exposure to the gases and solids formed upon combustion of a pyrotechnic composition contained within the pretensioner.  
           [0012]    In a preferred embodiment of the invention, the pretensioner contains a housing, a geared pulley or drive gear engaged with a geared clutch sleeve, a retractor shaft axially and longitudinally disposed within the geared clutch, a strap that rotates the drive gear upon pretensioner activation, a piston that tensions and impels the strap upon pretensioner activation, a gas generant or pyrotechnic that propels the piston, and an initiator that ignites the gas generant upon a signal from an accelerometer, for example. Upon ignition of the gas producing pyrotechnic, the piston is driven forward in an essentially linear path thereby tightening the strap and rotating the drive gear, and simultaneously rotating the geared clutch to facilitate a torque about the webbing reel shaft. Rotation of the geared clutch sleeve fixed over a first end of the webbing reel shaft thus effects pretensioning of a seat belt spooled about the webbing reel.  
           [0013]    After use, only the pretensioner or parts therein need be replaced, obviating the expense of also replacing the retractor or other components of the seat belt retraction mechanism. In general, the retractor is preserved for future use.  
           [0014]    Because expense heretofore associated with activation of a pretensioner is significantly reduced, passengers can be given the protection of seat belt pretensioning in even minor accidents. Moreover, a pretensioner that activates in minor collisions will also activate earlier in a severe crash sequence. Earlier activation of the pretensioner permits the pretensioner to operate less aggressively, reducing the possibility of injury caused by the seat belt pretensioner itself. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a diagrammatic elevational view of a replaceable seat belt pretensioner prior to activation, in accordance with the present invention.  
         [0016]    [0016]FIG. 2 is a diagrammatic elevational view of the replaceable seat belt pretensioner after activation, in accordance with the present invention.  
         [0017]    [0017]FIG. 3 is an elevational view of an embodiment containing a cover.  
         [0018]    [0018]FIG. 4 is a cross-sectional view of the embodiment in FIG. 3 taken along the line A-A, and illustrates the mechanical cooperation between a pretensioner clutch of the present invention and a state-of-the-art seat belt retractor.  
         [0019]    [0019]FIG. 5 is a cross-sectional view of the embodiment in FIG. 3 taken along the line B-B, and illustrates the mechanical cooperation between the strap and the geared pulley of a pretensioner of the present invention.  
         [0020]    [0020]FIG. 6 is a plan view of the clutch assembly spaced radially outwardly of the retractor shaft prior to pretensioner activation.  
         [0021]    [0021]FIG. 7 is a plan view of the clutch assembly compressed radially inwardly about the retractor shaft upon pretensioner activation.  
         [0022]    [0022]FIG. 8 is an elevational view of a preferred actuator.  
         [0023]    [0023]FIG. 9 is an elevational view of an embodiment containing a gas generator. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]    Referring to the figures, a pretensioner  10  in accordance with a preferred embodiment of the invention, comprises a gas generating composition  16  employed to pretension a seat belt  12  of a conventional seat belt retractor  14 . Typical seat belt retractors, to which the pretensioner of the present invention has application, are taught in U.S. Pat. Nos. 5,743,480, 5,553,803, 5,667,161, 5,451,008, 4,558,832 and 4,597,546, herein incorporated by reference. It should be emphasized, however, that although many known retractors employ clutch mechanisms upon pretensioner activation, the present invention obviates the need for clutch assemblies within the retractor used to pretension the seat belt. Pretensioners of the present invention contain a clutch assembly to improve and simplify the pretensioner drive as compared to other known pretensioners. Manufacturing of retractors associated with a pretensioner of the present invention may therefore be simplified.  
         [0025]    Housing  18  contains the gas generant  16 . Upon combustion, the gas generant  16  drives a piston  20 . The piston  20  is made from steel, brass, aluminum, plastic, or other sufficiently rigid material. If desired, a gas generator  22  may be contained within the housing  18  and employ the pyrotechnic material  16  for generating gas upon ignition thereof. The gas generant composition  16  may be any known pretensioner gas generant compound or alternatively, it may be any known gas generant useful in airbags, for example. To illustrate, see U.S. Pat. No. 5,035,757 herein incorporated by reference. Additionally, as shown in FIG. 1, the gas generant  16  may be contained within the piston  20  thereby eliminating the need for a separate generator  22 .  
         [0026]    Electrical contacts  24  on an initiator  26  communicate with a crash event sensor (not shown) that signals actuation of the pretensioner  10  upon a vehicle collision. Once the initiator  26  receives a signal, from an accelerometer for example, it ignites the pyrotechnic gas generant  16 . An initiator retainer  28  is threadedly or otherwise received within the housing  18  and houses the initiator  26 . Stated another way, a means for activating the pretensioner  10  and driving the actuator  20  upon a crash event includes the gas generant  16  contained within the piston  20  (or provided in a separate gas generator  22 ), the electrical contacts  24 , and the initiator  26 .  
         [0027]    Gas produced from combustion of the pyrotechnic gas generant  16  then propels the piston  20  into a flat portion  31  of a strap  30 . The strap  30  is spooled and anchored at a first end  32  around a drive gear or geared pulley  34 . A second end  36  of the strap  30  is preferably secured to the exterior of housing  18  at a point adjacent or proximate to the piston  20 . Drive gear  34  engages a geared clutch sleeve  38  during normal operation of the vehicle. Once the pretensioner  10  is activate, the torque exerted by tensioned strap  30  rotates gear  34  and geared clutch sleeve  38  engaged thereto. A first end  42  of a webbing reel shaft  40  is axially disposed within a clutch assembly  37  and rotates independently of the clutch assembly  37  prior to pretensioner  10  activation. A second end  44  of retractor axle  40  extends through the housing  18  and into the retractor  14 . A webbing spool or reel  46  in coaxial communication with the clutch assembly  37  rotates about the second end  44  for winding and unwinding of the seat belt  12 .  
         [0028]    A clutch  37  contains the geared clutch sleeve  38  compressively biased against a pair of fixed clutch segments  52  and  58 , wherein a rotary torque exerted upon clutch sleeve  38  in turn exerts a compressive and rotary torque upon segments  52  and  58  as they grip the shaft  40  upon pretensioner activation  10 . Although the Figures illustrate a preferred clutch, one of ordinary skill in the art will readily appreciate the possibility of employing other clutch designs in accordance with the present invention. Exemplary clutches are described in U.S. Pat. Nos. 5,451,008 and 5,743,480, herein incorporated by reference.  
         [0029]    As shown in the Figures, a first shear pin  50  fixes the corresponding first clutch segment  52  to the housing  18  and to a cover  56 . A second shear pin  54  fixes the corresponding second clutch segment  58  to the housing  18  and to the cover  56 . The geared clutch segments  52  and  58  are fixed apart and radially outwardly of the retractor axle  40  wherein each segment is circumferentially opposed to the other relative to the circumference of the shaft  40 . Stated another way, an inner surface  53  of arcuate segment  52  faces the inner surface  55  of arcuate segment  58  wherein the cylindrical shaft  40  lies therebetween. Conversely, clutch segments  52  and  58  are fixed radially inwardly of and in flush peripheral communication with an inner surface  39  of the geared clutch sleeve  38 .  
         [0030]    An axial cylinder or cylindrical portion  60  of pulley  34  accepts coiled or circumferential disposition of the strap  30  fixed thereto. Upon pretensioner activation and actuation of the piston  20 , the tensioned strap  30  exerts a torque about the cylinder  60  of the pulley  34 . As the torque increases responsive to linear movement of actuator  20 , the geared pulley  34  exerts a rotary torque upon the geared clutch sleeve  38  in geared communication therewith. The geared clutch sleeve  38  in turn initially exerts a compressive torque upon segments  52  and  58 . As the torque increases, the clutch sleeve  38  fractures respective shear pins  50  and  54 , thereby simultaneously imparting a rotary and compressive torque to the segments and rotatably driving the clutch segments  52  and  58  about the shaft  40 . As shaft  40  rotates, the webbing reel  46  correspondingly rotates and the seat belt  12  wound about the reel  46  is thereby pretensioned.  
         [0031]    In yet another aspect of the invention, a first rectangular channel  72  has a first end  74  and a second end  76 , and is formed longitudinally and substantially coextensive with the housing  18 . The actuator  20  is housed within the first end  74  prior to ignition of the propellant  22  and pretensioner  10  activation. A spring  77  may be employed to bias a leading edge of the actuator  20  against the flat portion  31  of the strap  30  that crosses the passage  72 . Noise due to vibration is thereby inhibited. The first end  32  of the strap  30  extends from portion  31  and is spooled about the cylindrical portion  60  of the pulley  34 . The second end  36  of strap  30  is fixed to the exterior of the housing  18  adjacent the piston  20 . When arranged in this manner, the strap  30  provides a motion multiplier effect comparable to that afforded by the use of geared motion multipliers such as planetary gears, but at a much lower cost. In sum, linear motion of the actuator  20  translates to rotary motions of the drive gear  34  and the geared clutch sleeve  38 , and rotary motion of the spool  46  in co-axial relation with the geared clutch sleeve  38 . The seat belt  12  is thus tightened.  
         [0032]    In essence, the present invention incorporates several motion multiplying features: 1) the piston  20 /strap  30  arrangement; 2) the two diameter geared pulley  34  (a smaller input diameter of cylinder  60  vs. a larger relative output diameter of geared portions meshed with sleeve  38 , wherein the input diameter or cylinder  60  has the strap  30  coiled and fixed about it); and 3) larger drive gear  34  output diameter vs. a relatively smaller clutch sleeve  38  diameter. Additionally, the present invention simplifies the design and manufacturing of known motion multipliers incorporating clutch mechanisms. Finally, an essentially sealed housing  18  prevents the release of relatively large quantities of gas, noise, and flame.  
         [0033]    To illustrate a retractor response based on pretensioner operation, see U.S. Pat. No. 5,899,399 to Brown et al., herein incorporated by reference. “Pretensioning” is generally defined to mean to take up slack in the seat belt. In accordance with the present invention, the gas produced by the gas generant propels the piston  20  into the strap  30  and thus affects rotary advancement of the hub  38  thereby tightening the slack in the seat belt  12 .  
         [0034]    2. Finally, in yet another aspect of the invention, it has been found that the use of a preferred actuator as shown in FIG. 8 results in a substantial increase in strap integrity during pretensioner activation. Certain known actuators employ one-piece slugs having a rounded leading edge formed at one end of a cylindrical slug, bar stock for example. As this type of actuator  20  impels the strap  30 , the strap  30  tends to deform about the rounded edge thereby weakening the strap at various points of deformation. This may lead to strap failure and pretensioner malfunction. On the other hand, an actuator  20  as shown in FIG. 8 includes a first cylindrical component  21  interlocked with a second component  23 , the second component forming a leading or rounded edge  29  of the actuator  20  and having a first flat side  25  and a second flat side  27  wherein the sides are joined by the rounded edge  29 , the rounded edge  29  in flush communication with the strap  30 . It has been found that upon pretensioner  10  activation, the surface area of the leading edge  29  in contact with the strap  30  is increased, by virtue of the flat sides  25  and  27 , thereby minimizing deformation and strap  30  failure.  
         [0035]    The housing  18 , the piston  20 , the drive gear  34 , the geared clutch sleeve  38 , the clutch segments  52  and  58 , and the initiator retainer  28  are preferably injection-molded, die cast, impacted, and/or machined from plastics, composites, and/or one or more metals such as steel, a steel alloy, zinc, or aluminum. The gas generating composition  16 , the gas generator  22 , the initiator  26  and the strap  30  are all manufactured or obtained by methods known to those of ordinary skill. Strap  30 , for example, may be formed from steel or aluminum strip, steel or aluminum cable, or fabric (cloth or rubber) strip. Companies such as Takata, Inc. of Japan may supply the gas generator  22 . The initiator  26  may be supplied by the original equipment manufacturer or from companies such as Special Devices Incorporated of Moorpark, Calif., for example. The aforementioned references are incorporated by reference and cited by way of example.  
         [0036]    Resultant benefits include simplified manufacturing and retractor preservation. For example, see U.S. Pat. No. 5,899,399 to Brown et al. Also see U.S. Pat. No. 5,397,075 to Behr, herein incorporated by reference, wherein relatively complex gear driving mechanisms used to actuate the retractor axle can be replaced by the present invention. Finally, gas ventilation ports as described in the cited references are not required (but may be provided if desired) and therefore manufacturing is even further simplified.  
         [0037]    While the foregoing illustrates and describes the use of the present invention, it is not intended to limit the invention as disclosed in certain preferred embodiments herein. Therefore, variations and modifications commensurate with the above teachings and the skill and/or knowledge of the relevant art, are within the scope of the present invention as described herein and as stated in the appended claims.