Patent Publication Number: US-2007120000-A1

Title: Seat belt retractor including an energy absorbing device

Description:
BACKGROUND  
      The present invention generally relates to seat belt retractors having energy-absorbing or dissipating mechanisms and more particularly to a multi-level load-limiting system.  
      A classic seat belt retractor only offers a modest degree of energy absorption, which occurs as a relatively stiff seat belt stretches as it is loaded by the occupant during an emergency.  
      For decades, torsion bars have been proposed for use in seat belt retractors as an energy absorbing mechanism. As the torsion bar is twisted and, thus absorbing energy during a vehicle emergency, the torque or force displacement (rotation) characteristic of the torsion bar quickly reaches a saturated region, which corresponds to its plastic range of operation. This somewhat constant characteristic provides a reaction torque at the retractor and provides a reaction force or load on the seat belt, which retards and controls the manner by which the seat belt protracts from the spool. One level of reaction forces may not be adequate to protect occupants of differing sizes. Consequently, it is desirable to provide a seat belt system with more than one load-limiting characteristic or one that can be changed or changes as dynamic conditions change.  
      The prior art discloses seat belt retractors having two dissimilar and remotely located torsion bars to achieve a multi-level of load limiting, while other prior retractors use a single torsion bar that is sub-divided into two torsion bar portions to achieve multi-level load-limiting operation.  
     SUMMARY  
      It is an object of the present invention to provide a multi-level energy-absorbing seat belt retractor.  
      In one embodiment, the retractor employs two energy absorbing (EA) mechanisms in which a sensor in the retractor initiates both mechanisms and a controller deactivates one of the mechanisms.  
      Another embodiment of the invention comprises two EA mechanisms in which one of the EA mechanism is triggered at about the same time by the other EA mechanism.  
      The first EA mechanism may include a torsion bar that generates a protective force for all occupants during low or high-speed crashes. The torsion bar reaction torque is set to a range as low as about 2 kN and as high as about 6 kN.  
      The second EA mechanism may include a pre-bent member, such as a flexible band. The band may be a high elongation metal wherein the energy is absorbed by a bending action as it is plastically deformed when rolled from the outer diameter to the inner diameter. This second EA mechanism generates a protective force when a 95th percentile occupant is using the system during frontal crashes at or above a first crash level. The default mode of operation of the invention is to use the pre-bent member.  
      As described below, one of the advantages of the invention is that the retractor is designed to automatically start off at a high level of energy absorption after the seat belt has been extended, such as during a crash. This advantage fulfills the need of providing a higher level of energy absorption during a high load impact event by using two EA mechanisms. The invention also may include a means for disabling the energy absorbing feature of the pre-bent member when an occupant of a slight size is using the seat belt system. More particularly, the invention may include a means for disabling the pre-bent member as a means for entering the torsion bar mode of operation. This aspect provides the advantage of sparing the pre-bent member mechanism of any detrimental effects due to its unnecessary use during a lower load impact.  
      One embodiment of the present invention utilizes the combination of the characteristics of a torsion bar and a pre-bent member to provide a multi-level seat belt load-limiting system.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary and exemplary 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  is a cross-sectional view, which illustrates many of the major components of an embodiment of the invention.  
       FIG. 2  shows an exploded view of many of the major components of an embodiment of the invention.  
       FIG. 3  is a schematic drawing of the safety restraint system that includes the retractor of the present invention.  
       FIGS. 4   a - c  are side views of the retractor when in an initial position before the crash event.  
       FIGS. 5   a - c  are side views of the retractor when the retractor is locked into position for a higher load crash event.  
       FIG. 6  is a side view of the retractor when the retractor is locked into position for a lower-load crash event.  
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
      By way of background, U.S. Pat. Nos. 6,863,235 and 6,106,013 are incorporated by reference herein in their entireties.  
      Reference is made to  FIG. 1 , which shows the major components of a seat belt retractor  100  incorporating the present invention. The retractor includes a frame  102  upon which a spool  106  is rotatably mounted between the sides  104   a ,  104   b  of the frame  102 . The sides  104   a ,  104   b  are mounted on the back  104   c  of the frame  102 . The spool  106  includes a central passage  108  for receipt of a torsion bar  112 . The retractor  100  is an emergency locking retractor or ELR, which can be coupled to an optional automatically locking retractor or ALR switching mechanism.  
      The torsion bar  112  includes two ends  114   a ,  114   b  that have notches about their periphery. The spool  106  has a mating hole that has mating grooves, which allows the end  114   a  of the torsion bar  112  to be inserted in the spool&#39;s hole. This connection allows the spool  106  and the torsion bar  112  to rotate in unison. The end  114   a  of the torsion bar is also connected to a rewind spring  118  through a spring arbor. The spring arbor (not shown) is commonly used to connect the rewind spring  118  to the torsion bar  112 . As the spool  106  is loaded, it twists the torsion bar  112  and rotates relative to the torsion bar. The twisting of the torsion bar generates a reaction force, which is used to control the payout of the seat belt during an accident. A quantity of the seat belt or webbing  122  (shown in dotted outline) is mounted or rotated onto the spool  106 . The spool flanges center the seat belt  122  on the spool.  
      A seat belt system using the present retractor will include a tongue, which is mounted to the seat belt and a buckle in which the tongue can be locked in place (not shown in the figures). As is known, the retractor  100  can be mounted within a vehicle seat or secured to the floor or one of the pillars of a vehicle.  
      In addition to the torsion bar  112 , the retractor  100  also includes a second energy-absorbing mechanism. This second energy-absorbing mechanism can be a pre-bent member  202 .  FIG. 2  shows the components of the retractor in an exploded view.  
      The retractor includes a first locking mechanism, or the torsion bar mechanism. As previously mentioned, the torsion bar  112  is connected to the spool  106  through the use of a notched end  114   a  inserted into a grooved mating hole in the spool. The end  114   b  of the torsion bar also has notches around its periphery, which is inserted into a grooved mating hole  213  in the lock base  212 . This mating of the end  114   b  and the lock base&#39;s mating hole allows the lock base to rotate in unison with the torsion bar  112 .  
      The lock base  212  comprises the mating hole  213 , a flange  215 , a cylindrical protrusion  217 , a notch  219  in the cylindrical protrusion  217 , and lock wheel attachment  221 . A lock base pawl  222  is attached to the lock base  212  at a pivot  506 , as shown in  FIG. 4 ( a ). The lock base pawl  222  sits inside notch  219  and includes a post  502  that is inserted into a slot  504  that is located in a lock wheel  204 , as shown in  FIGS. 2 and 5 ( c ). The lock base pawl  222  is also configured to engage the teeth of a lock ring  218  through the use of at least one tooth. During operation, it is this engagement of the lock ring&#39;s teeth with the lock base pawl that causes the torsion bar mechanism to start to yield.  
      The lock wheel  204  is fastened to the lock base  212  at lock wheel attachment  221  which protrudes through a center opening  124  of the lock wheel. It is noted that the lock wheel  204  is not structural in any way and is only pivotably mounted to the lock base  212 . The lock wheel  204  also includes teeth about its periphery, which are configured to be engaged by at least one lock tooth from a lock wheel pawl  310 .  
      A second lock mechanism includes a pre-bent member  202 , such as a strip. The pre-bent member  202  is attached to the spool  106  through the hook-shaped end  248  that fits in a corresponding slot  252  in the spool  106 . This slot is located at a cylindrical protrusion  203  which extends from a flange  205  of the spool  106 . As the one end of the pre-bent member  202  is placed in the slot  252 , the other end  250  of the pre-bent member  202  presses against a lock case  246 . The lock case  246  covers both the pre-bent member  202  and the spool&#39;s cylindrical protrusion  203  and abuts against the spool&#39;s flange  205 , as seen in  FIG. 1 . With this arrangement, as the pre-bent member  202  yields during use, it exerts a reaction force against a lug on the inside wall of the lock case  246 .  
      The lock case  246  has teeth around its periphery and they are adapted to be engaged by lever  238 . The lever  238  can be engaged to lock case  246  through the use of the lock ring  218 . As previously mentioned, the lock ring  218  has teeth on its inner diameter which are adapted to be engaged by the teeth of the lock base lock pawl  222 .  
      The lock ring  218  has two arms  230 ,  232 . The lever arm  230  has a hook-like end  234  and a lever spring  236  fits over it, as depicted in  FIG. 4 ( a ). The hook-like end  234  engages a lever arm  242 . The lock ring&#39;s other arm  232  is pushed by a return spring  240  in a clockwise direction. The lock ring  218  and the return spring  240  fit inside a case guide  228 , which includes suitable cut-outs to accommodate the lock ring  218 , the return spring  240 , and the lever  238 . These component are retained in the case guide&#39;s cut-outs by the side  104   b  for frame  102 , which abuts the case guide.  
      As shown in  FIG. 4 ( a ), the return spring  240  pushes the arm  232  causing the lock ring  218  to remain in its furthermost clockwise position. In this position, the hook-like end  234  pulls on the lever arm  242  on the lever  238  which, in turn causes the lever  238  to rotate around a pivot  244 . Thus, the lever  238  remains unengaged with the teeth of the lock case  246 .  
      The operation of seat belt retractor will now be discussed. The seat belt retractor is switchable from an initial high load to a lower load during a crash event. Both the torsion bar mechanism and the pre-bent member mechanism are engaged for the higher load. The torsion bar mechanism and the pre-bent member mechanism are triggered with the same locking mechanism at about the same time. This mode of operation is used for larger occupants. During lower loads, the pre-bent member mechanism is deactivated. This mode of operation is used for smaller occupants.  
      FIGS.  4 ( a )-( c ) show the retractor in its initial position before the torsion bar or pre-bent mechanism is engaged. The torsion bar  112  is connected to the lock base  212  on one end and connected to the spool  106  on the other end. During operation, the torsion bar  112 , the lock base  212 , and the spool  106  rotate together in unison because of the notches in ends  114   a ,  114   b  of the torsion bar and the mating holes in the spool  106  and the lock base  212 . The lock base pawl  222  rotates with the lock base  212  because of its attachment at pivot  506 . Also, the lock wheel  204  rotates with the lock base pawl  222  because of the pawl&#39;s post  502  protruding through slot  504 . In addition, the pre-bent member  202  spins with the spool  106  due to its attachment to the spool  106  at its hook-like end  248 . Thus, because of these interconnections, the torsion bar  112 , the lock base  212 , the lock wheel  204 , the pre-bent member  202 , and the lock case  246  all spin in unison with the spool  106 .  
      While these components rotate, the pawl  222  remains unengaged with the lock ring  218 . As a result, the lock ring  218  remains in its furthermost clockwise position due to the force of the return spring  240  acting on its arm  232 . This position causes the arm  230  to pull lever arm  242  which results in the lever  238  rotating around its pivot  244  in a clockwise fashion. Thus, lever  238  does not engage the lock case  246 .  
      The purpose of the torsion bar and pre-bent member mechanisms is to initiate the lock-up of the retractor in a crash or pending crash. To initiate the use of these mechanisms, a signal is received from at least one sensor placed in the vehicle, which are shown in  FIG. 3  as reference numerals  304 ,  306 , and  308 . Such sensors can include a vehicle sensor and/or a web sensor but any known vehicle and web sensing mechanisms can be used with the retractor  100 . After receiving and processing the signals from one or more sensors  304 ,  306 , and  308 , the controller  302  activates the lock wheel pawl  310  to engage the lock wheel  204 ; thus, stopping the rotation of the lock wheel  204 .  
      Even though the lock wheel  204  has stopped, the spool  106  continues to rotate. As depicted in  FIG. 5 ( a )-( c ), as the spool rotates, the pawl post  502  of the lock base pawl  222  rides up the lock wheel&#39;s slot  504 . As the post  502  slides, the pawl  222  rotates about its pivot  506 , which results in the teeth of the pawl  222  engaging the teeth of lock ring  218 .  
      The pawl  222  is the load bearing pawl and once it engages the lock ring  218 , it rotates the lock ring counterclockwise against the force of the return spring  240 . The lock ring  218  continues to rotate and compressing the spring until the lock ring  218  stops against the edge  510  of the case guide&#39; cut-out. The cessation of rotation of the lock ring  218  has two consequences, which is described below.  
      The first consequence is that, once the lock ring  218  stops rotating, the lock base  212  stops rotating because it is attached to the pawl  222  at the pawl&#39;s pivot  506 . Once the lock base  212  has stopped turning, the torsion bar&#39;s rotation also stops because of its attachment to the lock base  212  at the mating of end  114   b  and the mating hole  213 . Since the spool  106  is still free to rotate, the torsion bar twists because of its attachment to the spool on the one end and the stopped lock base on the other. This twisting of the torsion bar  112  absorbs the load.  
      The second consequence is that the rotation of the lock ring  218  causes the lock ring&#39;s arm  230  and the lever spring  236  to push the lever arm  242 . Because of this pushing from the spring  236 , the lever  238  rotates counter-clockwise about its pivot  244 , which results in the lever head  508  engaging the lock case  246 . With the lever head  508  so engaged, the rotation of the lock case  246  is halted while the spool  106  is still free to rotate.  
      As previously mentioned, the pre-bent member  202  presses against the lock case  246  at one end and is attached to the spool  106  at the other. Once the lever head  508  is engaged with the lock case  246 , pre-bent member  202  exerts a reaction force against the lug on the inside wall of the lock case  246  as the spool continues to spin; thus, causing the pre-bent member to absorb the load. In this position, in order to rotate, the spool must overcome the loads caused by the torsion bar  112  and the pre-bent member  202 , i.e., the torsion bar and pre-bent member begin to yield. In effect both the torsion bar and pre-bent members begin yielding at about the same time, or within a few degrees of rotation of the spool.  
      An occupant classification system of known type provides an output or control signal to identify whether the occupant (using the retractor) is a small (5th percentile) occupant or a larger occupant (greater than 50th percentile). Occupant classification systems while new are generally well known in the art. For example, the occupant classification system can include a weight sensor and associated electronics. Further, the occupant classification system determines that an accident is about to occur (crash sensor, radar or sonar sensors and associated electronics, which may be part of the occupant classification system) or has just begun.  
      Once the presence of a small occupant is determined, and if the vehicle is involved in an accident, the locking mechanism associated with the pre-bent member mechanism is deactivated by a signal from controller  302 . The controller can activate a pyrotechnic unit  602  that applies a force to lever arm  242  which compresses the lever spring  236  and rotates lever  238  clockwise about pivot  244 , as shown in  FIG. 6 . Once the lever pivots, the head of the lever  508  disengages from the teeth of the lock case  246 , which allows the lock case to rotate freely in unison with spool  106 . Thus, the spool will rotate only against the resistance of the torsion bar  112  since the pre-bent member will not be engaged.  
      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.