Abstract:
An electromechanical seat belt retractor has a seat belt retractor assembly having a spool rotationally moveable about an axis of rotation for winding and unwinding a seat belt; a motor for selectively rotating the spool; a clutch including an over-clutch driven by the motor through one or more gears; the clutch being coaxially aligned with the axis of rotation of the spool and linearly spaced from the spool; and wherein upon a forward actuation of the motor a clutch plate of the clutch linearly moves to engage the spool coupling to the spool and thereafter rotating the spool about the axis to initiate a winding of the seat belt. After the clutch plate engages the spool a reversal of the motor linearly moves the clutch plate away from the spool disengaging the spool. Preferably the clutch means is a Bendix type clutch assembly. In a preferred embodiment, the clutch plate first engages an over-clutch is fixed in a locking engagement to the spool.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a seat belt retractor generally. More particularly to seat belt retractors of an electromechanical type which use an electric motor to wind up the seat belt in various situations including when a collision event is imminent to more securely hold the occupant just prior to and during impact. 
       BACKGROUND OF THE INVENTION 
       [0002]    A seat belt device installed in a vehicle such as an automobile typically has at least a seat belt retractor for winding up a seat belt, a tongue slidably attached to the seat belt, and a buckle to which the tongue can be latched. In the event of an emergency such as a vehicle collision where a large deceleration is exerted on the vehicle while an occupant wears the seat belt in a state that the tongue is latched to the buckle, the seat belt device restrains, thereby protects the occupant. 
         [0003]    The seat belt device is provided with a seat belt retractor for winding up the seat belt. The seat belt retractor has a biasing means such as a spiral spring which always biases a spool, on which the seat belt is wound, in the belt-wind up direction. When not used, the seat belt is fully wound on the spool by the biasing force of the biasing means. When used, the seat belt is withdrawn against the biasing force of the biasing means and is worn by the occupant. In the seat belt retractor, a locking mechanism is activated in the event of emergency as mentioned above to stop the rotation of the spool in an unwinding direction, thereby preventing the seat belt from being withdrawn. 
         [0004]    A motorized seat belt retractor has a motor to wind up the spool and is commonly referred to as an EMR or electro mechanical retractor. When it is determined that the collision is imminent as well as in other operating situations, the tension on a seat belt is increased by increasing the driving force of a motor to wind up the seat belt, thereby increasing the restraint force of the occupant and, when the vehicle collision is actually detected, an additional pretensioner can be actuated whereby the seat belt is rapidly wound up, thereby further increasing the restraint force for the occupant. 
         [0005]    A variety of EMR type seat belt retractors are commercially sold, but in every type sold, in the event no collision occurs the predetermined or otherwise tightening of the seat belt must either be reversed or otherwise disengaged. 
         [0006]    Ideally, seat belt retractors need to be sophisticated in performance and yet simple and reliable in design. The coupling of an electric motor to the seat belt retractor provides opportunities to improve the performance of the seat belt system to better secure the occupant prior to a collision but it has also created additional cost, complexity issues that need to be solved. 
         [0007]    The present invention provides a novel way to insure high quality performance while improving reliability and reducing the cost to manufacture the device. 
         [0008]    The invention as described herein provides a novel way to engage and disengage the various electro mechanical elements so that the belt wind up forces are safely and efficiently transmitted from the motor more directly to the spool while bypassing the more fragile components in the retractor assembly. The invention also further provides a way to simply disengage the motor from the mechanism such that the retractor assembly can function virtually independent of the motor during normal driving conditions. 
       SUMMARY OF THE INVENTION 
       [0009]    An electromechanical seat belt retractor has a seat belt retractor assembly having a spool rotationally moveable about an axis of rotation for winding and unwinding a seat belt; a motor for selectively rotating the spool; a clutch means driven by the motor through one or more gears; the clutch means being coaxially aligned with the axis of rotation of the spool and linearly spaced from the spool; and wherein upon a forward actuation of the motor a clutch plate of the clutch means linearly moves to engage the spool coupling to the spool to the motor and thereafter rotating the spool about the axis to initiate a winding of the seat belt. After the clutch plate engages the spool a reversal of the motor linearly moves the clutch plate away from the spool disengaging the spool. The clutch plate can directly engage the spool or preferably indirectly engage the spool using an intermediate over-clutch attached to an end of the spool to cause a direct locking engagement with the spool. In the illustrated embodiment, the clutch means is a Bendix type clutch assembly. In the illustrated embodiment, the clutch plate first linearly moves to engage an over-clutch pre-attached to the spool causing a locking engagement of the spool. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The invention will be described by way of example and with reference to the accompanying drawings in which: 
           [0011]      FIG. 1  is a perspective view of the electromechanical retractor (EMR) assembly according to the present invention. 
           [0012]    FIG.&#39;S  2 A and  2 B are exploded views of the electromechanical retractor assembly take from  FIG. 1  showing the various components of the assembly. 
           [0013]      FIG. 3  is a cross sectional view of the electromechanical retractor assembly showing the linearly moveable clutch means in the pre-engagement location. 
           [0014]      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. 
           [0015]      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. 
           [0016]      FIG. 5A  is an enlarged exploded view of the spool and clutch mechanism. 
           [0017]      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. 
           [0018]      FIG. 6  is a perspective view of the clutch mechanism assembly with the one cover removed to show the components. 
           [0019]    FIG.&#39;S  7 A and  7 B 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. 
           [0020]      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. 
           [0021]      FIG. 9A  is a cross sectional view of the seat belt assembly taken along lines  9 A- 9 A of  FIG. 8 . 
           [0022]      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 
       [0023]    With reference to  FIG. 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. 
         [0024]    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 . 
         [0025]    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. 
         [0026]    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. 
         [0027]    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. 
         [0028]    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 . 
         [0029]    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 . 
         [0030]    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. 
         [0031]    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. 
         [0032]    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 . 
         [0033]    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.