Abstract:
A seat belt retractor device has a gas generator for generating a high pressure gas when a vehicle is in emergency; a chamber cylinder for conducting the high pressure gas from the gas generator; a piston received movably within the chamber cylinder and pressed and moved by the high pressure gas, the piston having an O ring sealed end portion engaging walls of the chamber cylinder and a rack portion extending into the chamber cylinder; and a drive unit for rotating a winding shaft or spool of a seat belt retractor in a direction of removing a slack of a belt, using the movement of the piston and driven by said rack teeth portions; a pretensioner employed with an energy absorbing mechanism, for reversely rotating the winding spool when a tension acting on the belt exceeds a predetermined value after removing the slack of the belt; and a venting mechanism having a gas passageway for exhausting the high pressure gas from a space filled with the high pressure gas to the outside of the space, the gas passageway extending through the sealed end portion into said rack, characterized by the gas passageway having a first longitudinal extending passageway portion extending for a length in the direction of the rack portion to a closed end and a second transverse passageway portion intersecting the first portion at a distance of at least 10 mm from the end, and being open to the outside space.

Description:
FIELD OF THE INVENTION  
       [0001]    The present invention relates to a seat belt retractor generally. More particularly to seat belt retractors with a pretensioner device used with an energy absorbing device. 
       BACKGROUND OF THE INVENTION  
       [0002]    Seat belt retractors have been designed to respond to an emergency such as a collision by activating a pretensioner that quickly takes up the slack in the seat belt webbing to tightly secure the occupant. After this rapid tightening has occurred, it has been found desirable to provide an energy absorbing device such as a torsion bar inside the retractor which allows the webbing to be retracted in response to the forces of the occupant&#39;s weight being pulled forward by the inertia forces generated by the rapid deceleration of the vehicle and the forward momentum of the occupant. This responsive action of energy absorption puts less stress o the webbing and the occupant and is a highly desirable feature in the event of a collision. 
         [0003]    To achieve the rapid action needed in terms of winding the webbing about the spool of the retractor a pretensioner device having a piston and a chamber are employed using a gas generator, typically pyrotechnic device that fires generating a rapid rise in gas pressure which pushes the piston in the chamber, the piston has a toothed rack that spins a mating toothed pinion gear to rotate the spool, thereby removing the slack in the seat belt. These pretensioners are extremely reliable and very fast in achieving the desired objective of slack removal, however, once activated, the gasses entrapped behind piston and the chamber create an additional resistance to the proper functioning of the energy absorbing device such as a torsion bar, and thus impede its ability to allow the webbing to unwind properly. 
         [0004]    This problem is well described in EP 1243487 A2 entitled “Seat Belt Device” and in U.S. Pat. No. 6,575,498 B2 entitled “Webbing Retractor”. Both of these patents describe the problem of entrapped gasses from a pyrotechnic gas generator type pretensioner. Each provides a unique way of providing a gas venting mechanism that allows the gases to pass through the sealed end of the piston internally into a rack portion of the piston where it is vented or exhausted to relieve the gas pressure and to allow the energy absorbing device to perform its function without added resistance. 
         [0005]    A primary problem in each of these prior art disclosures is the performance of the gas vents can be degraded or even stopped completely if the relatively small vent passages become blocked. In EP 1243487 A2 the end of the piston has a very small orifice and the gasses must first pass through that to thereafter expand prior to venting. The use of a pyrotechnic charge is known to exhibit a gas mixture having burnt particulates or metal debris that can partially block or even occlude the entire opening. This can create a degree of unreliability that is unacceptable in such a device. 
         [0006]    In U.S. Pat. No. 6,575,498 larger diameter openings are used to create vent passageways, but these require the use of air or gas barricades or plugs to insure not too much gas is vented prior to initiating movement of the pretensioning piston. These barricades or plugs must be removed from the passages to allow venting to occur. As can be appreciated the complexity and timing issues of such a system add to more reliability issues. 
         [0007]    The need to reliably exhaust gas to allow the piston to move back down the chamber as the energy absorbing torsion bar tries to allow the webbing to unwind is critical. 
         [0008]    The gas venting ideally should occur automatically without requiring additional components and debris blockages of the vent passages must be prevented. 
         [0009]    These and other features of the present invention are provided in the description that follows. 
       SUMMARY OF THE INVENTION  
       [0010]    A seat belt retractor device has a gas generator for generating a high pressure gas when a vehicle is in emergency; a chamber cylinder for conducting the high pressure gas from the gas generator; a piston received movably within the chamber cylinder and pressed and moved by the high pressure gas, the piston having an O ring sealed end portion engaging walls of the chamber cylinder and a rack portion extending into the chamber cylinder; and a drive unit for rotating a winding spool of a seat belt retractor in a direction of removing a slack of a belt, using the movement of the piston and driven by said rack portions; a pretensioner employed with an energy absorbing mechanism, for reversely rotating the winding spool when a tension acting on the belt exceeds a predetermined value after removing the slack of the belt; and a venting mechanism having a gas passageway for exhausting the high pressure gas from a space filled with the high pressure gas to the outside of the space, the gas passageway extending through the sealed end portion into said rack, characterized by the gas passageway having a first longitudinal extending passageway portion extending for a length L of about 20 mm or greater in the direction of the rack portion to closed end and a second transverse passageway portion intersecting the first portion at a distance of at least 10 mm from the end, and being open to the outside space. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0011]    The invention will be described by way of example and with reference to the accompanying drawings in which: 
           [0012]      FIG. 1  is a perspective view of the electromechanical retractor (EMR) assembly according to the present invention. 
           [0013]      FIGS. 2A and 2B  are exploded views of the electromechanical retractor assembly take from  FIG. 1  showing the various components of the assembly. 
           [0014]      FIG. 3  is a cross sectional view of the electromechanical retractor assembly showing the linearly moveable clutch means in the pre-engagement location. 
           [0015]      FIG. 4A  is an enlarged cross sectional view of the electromechanical retractor assembly showing the linearly moveable clutch means prior to engaging an over clutch. 
           [0016]      FIG. 4B  is a cross sectional view of linearly moveable clutch plate engaged to the over clutch wherein the clutch plate is pushed into contact with an end of the spool containing a locking means comprising a plurality of spring loaded balls adapted to lock into recesses in an end of the over clutch. 
           [0017]      FIG. 5A  is an enlarged exploded view of the spool and clutch mechanism. 
           [0018]      FIG. 5B  is a second enlarged exploded view of the spool and clutch mechanism from another perspective showing the other side of the various components. 
           [0019]      FIG. 6  is a perspective view of the clutch mechanism assembly with the one cover removed to show the components. 
           [0020]      FIGS. 7A and 7B  show the spool and clutch assembly,  FIG. 7A  showing the rotation to engage the overclutch and spool, while  FIG. 7B  shows the opposite rotation causing a disengagement of the clutch from the over clutch and spool. 
           [0021]      FIG. 8  is a perspective view of the seat belt assembly according to the present invention showing a pretensioner assembly attached to a side of the frame. 
           [0022]      FIG. 9A  is a cross sectional view of the seat belt assembly taken along lines  9 A- 9 A of  FIG. 8 . 
           [0023]      FIG. 9B  is the cross sectional view of  FIG. 9A  after the pretensioner assembly has been activated demonstrating an emergency crash scenario. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    With reference to  FIGS. 1 ,  2 A and  2 B.  FIG. 1  is a perspective view of an electromechanical seat belt retractor  100  according to the present invention is illustrated. The seat belt retractor  100  as shown has a frame  40  which holds a spool  50  between two opposing sides  41 ,  42  of the frame  40 . Attached to the left hand side of the seat belt retractor assembly  100  is a spring biasing assembly  60  which includes a spirally wound pretensioned spring  62  that provides a bias to the seat belt retractor assembly  100  so that the seat belt (not shown) is always biased in the wound up position. As a user operates the seat belt by pulling on the seat belt, the spool  50  rotates and the seat belt is pulled outwardly increasing the tension on the biasing spring  62 . Interposed between the spring biasing assembly  60  and shown also on the lower left hand side  41  of the frame  40  is a pretensioner mechanism  80  which in an emergency crash situation can be fired to activate a rapid pretensioning of the spool  50  causing an immediate take up of the seat belt to more securely hold the occupant. 
         [0025]    With reference to the right hand side  42  of the frame  40  of the seat belt retractor assembly  100  an outer dust cover  70  is illustrated which covers a spool locking mechanism of known construction that includes an inertial vehicle sensor and web sensor. The locking mechanism includes lockcup  74  that is rotationally supported on an axle such as a portion of the torsion bar. The lockcup  74  supports a housing  71  which supports a moveable weight sensor or mass  72 . The locking mechanism includes a locking pawl  73  rotationally mated with a frame side  42  and a lock wheel as well as other known components that will provide a mechanical path in which the spool  50  can be locked from further rotation outwardly during periods of high vehicle deceleration and/or periods of rapid protraction of the seat belt from the spool. Interposed between the dust cover  70  and the seat belt retractor frame  40  is a two piece clutch housing cover  29 A and  29 B which contains a clutch means  10  that can be activated by an electric motor  30  as shown in  FIG. 2B . 
         [0026]    With further reference to  FIGS. 2A and 2B , an exploded view of the entire seat belt retractor assembly  100  is illustrated showing the various components that are used to make the entire assembly. With reference to the upper portion of  FIG. 2A  the spring biasing assembly  60  as illustrated, a spirally wound biasing spring  62  is pre-wound using a prewinding clip  61  and is attached to the spring cover  66  which is connected to the housing  63  in such a fashion that a biasing force is always applied to the spool  50  after the prewinding clip  61  is removed. The spring  60  is connected to one end  76 A of a torsion bar  76  by a spring arbor  65  in a known manner. The entire assembly  60  is then mounted and attached to the frame  40 . In between the spring biasing assembly  60  and the frame  40  is a clutch bracket  90  as illustrated which holds a clutch housing  92 , a locking pawl  94  an o-ring  96  and a retainer washer  98 . As further illustrated a pretensioner mechanism  80  including a cap  81 , a shorting clip  82 , a gas generating device  83  and a manifold  84  is illustrated. The manifold  84  houses a rack  85 , an o-ring  86  and a push retainer  87  that are connected to the frame  40  of the seat belt retractor assembly  100  in such a way that during a crash, the gas generating device  83  can be ignited and the rack  85  will engage the clutch housing  92  which drives end  76 A of the torsion bar  76  causing a rapid rotation of the spool  50  thus pretensioning the attached seat belt. 
         [0027]    As shown in the lower portion of  FIG. 2A , on the left hand side of the retractor frame  40  is a mechanical bushing  78 , a toothed pilot wheel  77 , the torsion bar  76  which extends on one side through a pilot wheel and extends on another side to the lockcup  74 . A thrust washer  75  is received on the torsion bar an inertia disk  79  which is part of the weight sensor  72 , a calibration spring  210 , a return spring  204 , a blockout cam  206  and an activation disk  105  vehicle sensor pawl  73 , a housing  101  connected by a pivot pin  106  as illustrated. A pin  202 , lockbar  201  and DRL wire  200  are shown along with a web sensor pawl  203 , a calibration spring  210  and return spring  204 , an activation disk  205 , blockout cam  206  and other miscellaneous elements  207 ,  208  and  209  are shown, some of which are optional accessories not required in using the present invention per se, but are illustrated to show the entire retractor assembly  100 . These mechanisms are commonly used in mechanical seat belt retractors and are understood by those of ordinary skill in the art to provide a way of locking the spool  50  during a rapid seat belt protraction and rapid vehicle deceleration which would cause the web sensor to activate or the sensor weight  72  to tip causing the sensor pawl  73  to pivot which initiates the locking of the spool  50  which is not free to rotate relative to the torsion bar  76  and any applied force on the torsion bar  76  could be absorbed thereby. 
         [0028]    As shown in  FIGS. 2B and 3 , one of the unique features of the present invention is the use of a motor  30  attached to a clutch means  10 . The motor  30  is attached to the lower portion of the seat belt retractor  100  and is encased in a motor sleeve  31 . The motor is also attached to the clutch means  10  which is entirely encased within a first clutch cover portion  29 A and a mating second clutch cover portion  29 B. As illustrated the drive axle  32  of the motor  30  is attached to a pinion gear  33  which drives a plurality of cluster and idle gears  35 ,  36 ,  37  each cluster gear  36  and idle gears  35 ,  37  are mounted and physically attached through the cover portions  29 A to the frame side  42  using cluster and idler pins  38  as illustrated. The pins  38  are then threadingly engaged using the screws  39  as illustrated. These gears  33 ,  35 ,  36 ,  37  connected directly to the motor  30  are connected to a ring gear  34  of the clutch means  10  which is coaxially aligned with the axis of rotation R (shown in  FIGS. 2A ,  2 B,  3  and  4 A) of the spool  50 . As further illustrated in  FIG. 2B  as well as in  FIGS. 5A and 5B , the ring gear  34  has a plurality of recesses  110  on an inner diameter into which protrusions  111  on a tubular shaped cylindrical ring  20  is pressed, this ring  20  has an outside diameter with a helix type of thread  21  shown on its outer surface. Attached to this ring  20  is a clutch plate  12  having an inside diameter with a complimentary threaded helix thread  11  that mates to the ring  20  in such a fashion that as the ring gear  34  is turned by the motion of the motor  30 , the clutch plate  12  can move along and be moved by the helix thread  21 . This is made possible by the use of a drag wire  8  (shown in  FIGS. 3 ,  4 A and  4 B) wrapped around the outer circumference of the clutch plate  12  as shown in  FIG. 6 . The drag wire  8  is a spring type device that provides frictional drag on the clutch plate  12 . When assembled into the clutch cover portions  29 A and  29 B as shown in  FIG. 4A , the drag wire  8  is not free to rotate as the ring gear  34  and ring  20  rotate, accordingly, the clutch plate  12  will be driven inwardly absent any rotational motion until it approaches the end of the threaded helix portion  21  of the ring  20  in which fashion it will then initiate an increased torsional force which overcomes the drag friction on the drag wire  8  and enables the clutch plate  12  to rotate freely inside the drag wire  8 . As a portion of the drag wire  8  is being moved linearly inward and by the forward motion of the motor  30  an over-clutch  14  is engaged as shown in  FIG. 4B . The over-clutch  14  as illustrated has a plurality of recesses  16  shown in  FIG. 5A  on a first side  14 A of the over-clutch  14 , as the clutch plate  12  approaches it, teeth  13  on the clutch plate  12  engage these recesses  16  in such a fashion that the clutch plate  12  continues to move towards the spool  50  until the teeth  13  of the clutch plate  12  are fully engaged within the arcuately elongated recesses  15  of the over-clutch  14 , as the over-clutch  14  is then rotated along with the spool  50  by the clutch plate  12 . As can be seen in  FIGS. 5B and 3 , the spool  50  has an end  51  with a plurality of holes  52  adapted to accept an over-clutch springs  53  in each hole location  52  and one of a plurality of balls  54 , preferably ball bearings  54  is positioned between the over-clutch spring  53  and the over-clutch  14 . On one side of the over-clutch  14  there are a plurality of recesses  15  correspondingly aligned with the holes  52  in the end of the spool  50 . Upon assembly to the spool  50  the over-clutch  14  has these recesses  16  come into alignment with the holes  52  wherein the spring loaded ball bearings  54  are moved inwardly into the recesses  15  on the over-clutch  14  creating a locking engagement between the over-clutch  14 , and the spool  50 . The over-clutch  14  being held against the spool  50  by a retainer clip (not shown). As illustrated in  FIGS. 4B and 7A , when the spool  50  is rotated by the movement of the drive motor  30  in a direction to affect seat belt retraction, which is accomplished by rotation of the gears  33 ,  35 ,  36 ,  37  being connected to the ring gear  34  causes the clutch plate  12  to move linearly inward and engage the over-clutch  14  which in turn being fixed to the spool  50  creates the motion necessary to initiate rotation of the spool  50  to tighten the seat belt. The activation of the motor  30  can occur in many situations including non-crash situations to retighten a loose seat belt about an occupant or when a sensor indicates that a crash appears imminent which causes a signal to be sent to the electronic control unit  120  to activate the motor  30 . In such a condition the seat belt will pretighten to ensure that the occupant is in a safe position and properly secured prior to impact. Should a collision occur which may be sensed by another sensor, the pretensioner mechanism  80  will activate to cause a significant increase in pretension forces to occur further driving the spool  50 . However, in many occurrences the use of a motor  30  is provided in the event that an incipient crash (rapid vehicle deceleration) is sensed wherein the prepositioning of the seat belt and the occupant is desirable. Therein comes the use of the electric motor  30  and the clutch means  10  according to the present invention. What is unique about this device  100  is that motions are all incurred and engagement of the spool  50  occurs through a linear movement that is coaxial with the axis of rotation of the spool  50  which means that the clutch plate  12  can engage the spool  50  through the over-clutch  14  in such a fashion that it creates a secure locking system that is independent of the other mechanism throughout the retractor assembly  100 . This is important in that loads and overloads of the fragile plastic components used throughout the mechanism can be avoided in that a direct linkage is created between the spool  50  and the clutch means  10  and gearing of the electric motor  30  are independent of the other mechanism. This ensures that the seat belt is capable of being pretensioned, by the pretensioner mechanism  80 , without unduly loading any of the other components of the device  100 . Secondarily by reversing the motor  30  as shown in  FIG. 7B , the seat belt can be unwound and the clutch means  10  will revert back along the helix thread  21  of the ring  20 , such that as the clutch plate  12  pulls back away from the spool  50  and the pre-attached over-clutch  14  which enables the entire motor-clutch mechanism to disengage from the spool  50 . Once this occurs, the clutch means  10  is totally isolated from the normal operation of the retractor assembly in such a fashion that the electromechanical seat belt retractor assembly can operate as a conventional seat belt retractor without any drag or resistance created by the motor or clutch means  10 . This is quite useful in ensuring that none of the mechanical systems that are normally used within a seat belt retractor assembly need to be modified for the incorporation of the motorized clutch means  10 . This ensures that there is no additional drag caused by the clutch  10  which is provided without interfering with the normal operation of the seat belt retractor assembly. What is particularly unique about the motor initiated, linear movement of the clutch means  10  is that the entire clutch means can be positioned in a very nominal amount of space. As shown, the entire clutch means  10  is located inside the side  42  of the seat belt frame  40  and the mechanical weight sensing mechanisms are located inside the dust cover  70  that are normally attached to such a retractor device. This means that the entire clutch means  10  is provided in a very compact and efficient assembly occupying a very limited amount of space which is extremely important when providing seat belt retractors with this level of performance capability or complexity. 
         [0029]    With reference to the pretensioner device, attention is called to  FIGS. 8 ,  9 A and  9 B. In  FIG. 8 , the pretensioner mechanism  80  is shown attached to the frame  40  of the seat belt retractor  100 . 
         [0030]    The pretensioner mechanism  80  has a cap  81  threadingly attached. The cap  81  has an opening exposing a shorting clip  82  to which a wiring harness (not shown) can be attached. The shorting clip  82  is attached to a pyrotechnic gas generator device  83  that includes a propellant charge and an igniter squib as shown in  FIG. 9A . The gas generator device  83  is shown stored in a transverse chamber portion  84 B of the manifold housing  84 . In a longitudinal chamber portion  84 A is housed a piston  85 . The piston  85  has an enlarged flanged end portion  85 C with an O ring type seal  131  for air tightly engaging the walls of the longitudinal chamber portion  84 A. A rack portion  85 A extends outwardly from the flanged end portion  85 C. On one side of the rack portion  85 A there are a plurality of gear teeth  85 B. The gear teeth  85 B engage pinion gear  92 A which has gear teeth  92 B that intermesh with the teeth  85 B of the rack  85 A when the pretensioner device is activated to move the piston  85  up the longitudinal chamber  84 A causing the pinion gear  92 A to rotate moving the spool  50  to take up any belt slack. As shown in the opening through the pinion gear  92 A is the end of energy absorbing device such as torsion bar  76 . 
         [0031]    As further shown in  FIG. 9A  is a first large longitudinal extending passageway  85 D that extends partially through the lower portions of the piston  85 . This passageway extends a substantial distance into the rack portion  85 A to a closed end  85 F. The length of the passageway  85 D is at least 20 mm and the cross sectional area A L  is generally uniform along the length L and is preferably at least 12.6 mm 2 , as shown the cross section is circular having a diameter D L  of at least 4 mm. 
         [0032]    A second passageway  85 E intercepts with the first longitudinal passageway  85 D. The location of the passageway  85 E may vary relative to the length of first longitudinal passageway  85 D. As illustrated the intersection point is approximately halfway up the length of the first longitudinal passageway  85 D. The passageway  85 E is an exhaust passageway and is open on at least one end to the chamber  84 A such that gasses produced by the pyrotechnic element can pass to reduce the gas pressure in chamber  84 B. As shown the transverse vent  85 E can pass through one or both sides of the rack  85 A and the passageway  85 E is very small in comparison to the cross-sectional area of the first passageway  85 D. The total area A T  of one or two of the second passageway is less than 7% of the area A L  of the first passageway  85 D. As shown the cross-sectional area A T  is 0.8 mm 2  and is of a circular cross section having a diameter D T  of about 1 mm when only one exhaust vent is used. The diameter D T  is less than 1 mm when two such passageways  85 E are employed. 
         [0033]    With reference to  FIG. 9B  when the pyrotechnic gas generator  83  is ignited the gas  300  pushes the piston  85  thrusting it upward into the chamber  84 A causing the pinion gear  92 A to rotate the spool  50  removing the web slack. Upon ignition of the propellant in addition to gas  300  from the propellant, the small amount of solid debris  301  is created. This solid debris is propelled up into the first longitudinal passage  85 D moving very rapidly past the transverse passage  85 E and impacting in the end  85 F of the first passageway  85 D creating turbulence. This debris  301  is lodged in the end  85 F of the first passageway  85 D at least during the time that gas is being generated by the pyrotechnic element  83  and as such the debris  301  tend not to block or impede the gas venting through the second transverse passageway  85 E. The continued build up of gas pressure creates a blocking action holding the debris  301  against the end  85 F as the gas  300  vents through the side or transverse passageway  85 E. Thus by providing a sufficiently large holding space in the volume of  85 D beyond the transverse passageway  85 E, all the debris  301  are entrapped by the onflow of gas  300  trying to leave through the second transverse passageway  85 E. As shown in  FIG. 9A , the gas venting second passageway  85 E is located a distance X of at least 10 mm from the closed end  85 F. Similarly the diameter of the first passageway  85 D is at least 4 times greater than the diameter of the second transverse passageway  85 E, resulting in an area difference wherein the area A L  is preferably about 10 times greater than the total area A T . 
         [0034]    Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.