Abstract:
A seatbelt retractor assembly ( 10 ) has a seatbelt retractor ( 14 ) and an actuator ( 26 ) for locking and unlocking the seatbelt retractor ( 1 ). An inertial sensor mass ( 30 ) detects changes in vehicle speed. The mass ( 30 ) has a guide surface ( 34 ) for interacting with the actuator ( 26 ). The guide surface ( 34 ) moves between an unlocking position ( 38 ) in which the actuator ( 26 ) unlocks the seatbelt retractor ( 14 ) and a locking position ( 42 ) in which the actuator ( 26 ) locks the seatbelt retractor ( 14 ). The actuator ( 26 ) has an actuator arm ( 25 ) with a surface contacting portion ( 54 ) in contact with the guide surface ( 34 ) and an open slot ( 57 ) above the surface contacting portion ( 54 ). The surface contacting portion ( 54 ) is connected to the actuator arm ( 25 ) by a beam structure ( 56 ) having a spring rate K beam  sufficient to maintain the open slot ( 57 ) open during normal vehicle operation.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a seatbelt retractor assembly.  
       BACKGROUND OF THE INVENTION  
       [0002]     A seatbelt for a passenger vehicle typically has a seatbelt retractor that serves to retract the belt into its housing. The belt is wound upon a spool in the housing. When the belt is drawn or protracted from its housing, the spool winds a retraction spring, which later retracts the unused portion of the belt onto the spool or withdraws the belt into its housing when not in use.  
         [0003]     In the event of a crash, the seatbelt retractor has a lock that prevents the seatbelt from extending further from its housing. The lock may be actuated by an inertial sensor, which responds to changes in vehicle speed during the crash. When a large deceleration is detected, the inertial sensor triggers the lock of the seatbelt retractor to lock the spool and thereby secures the safety belt in place during the crash.  
         [0004]     The inertial sensor has an inertial sensor mass that moves in response to changes in speed of the vehicle. This mass is mechanically linked to the lock by an actuator. When the mass moves, the actuator moves and causes movement of a locking pawl that locks the lock when the mass has moved in excess of a predetermined amount. The actuator rests on a surface of the mass. This surface is typically angled so that movement of the mass causes rapid movement of the actuator and consequently the locking pawl. While rapid movement of the components of the inertial sensor and lock are desirable for safety, this same feature causes undesirable noise during normal vehicle operation. Another source of retractor rattle involves intermittent contact between the sensor actuator and the sensor mass as the actuator bounces on the guide surface of the sensor mass, a rattle noise can be heard. Typically, this noise can be reduced by cushioning the guide surface with a soft material. This, however, can reduce the sensitivity of the sensor mass by creating undesirable friction between the contacting surfaces of the actuator and the guide surface. As an alternative noise absorbing wraps around the retractor assembly have been added which reduce audible noise levels in the passenger compartment of the vehicle. These solutions increase cost and in some cases reduce the inertial sensor&#39;s responsiveness.  
         [0005]     A need therefore exists for a seatbelt retractor that reduces noise from the foregoing moveable parts.  
       SUMMARY OF THE INVENTION  
       [0006]     Like existing seatbelt retractor assemblies, the invention has an inertial sensor that detects changes in vehicle speed. The inertial sensor has an inertial sensor mass, which is linked to a seatbelt retractor locking pawl by an actuator. The actuator moves with the mass by riding on its surface. The inventor has discovered that a significant amount of noise arises from movement of the actuator and components linked to it. Accordingly, in contrast to conventional designs, the actuator is modified to add a slight springiness to the contact sensor portion in a manner that removes objectionable high frequency noise.  
         [0007]     The inventive seatbelt retractor assembly has a seatbelt retractor, an actuator for locking and unlocking the seatbelt retractor, and an inertial sensor mass for detecting changes in vehicle acceleration. The inertial sensor mass has a guide surface for interacting with the actuator. The guide surface is movable between an unlocking position wherein the actuator unlocks the seatbelt retractor and a locking position wherein the actuator locks the seatbelt retractor.  
         [0008]     The actuator has a pivotal actuator arm with a surface contacting portion resting on said guide surface of the sensor mass and an open slot above the surface contacting portion.  
         [0009]     The surface contacting portion is connected to the pivotal actuator arm by a beam structure. The surface contacting portion has a generally rounded or substantially hemispherical protruding bottom for contacting the guide surface. The open slot above the surface contacting portion extends above the generally rounded bottom portion and the beam structure.  
         [0010]     The connecting beam structure has a spring rate K beam , K beam  being sufficient to keep the open slot open during normal sensor vibration. This enables the beam to be sufficiently spring like and is designed to have an oscillating frequency f defined in  Elements of Vibration Analysis , L. Meirovitch, 1986 by  
         f   =       1     2   ⁢   π       ⁢         K   beam       m   eff             ,       
 
 wherein m eff  equals F static /gravity, as seen in  FIG. 3A . 
 
         [0011]     The actuator can be made of plastic and molded as a unitary structure having an effective mass m eff  with the open slot geometry optimally selected by using the parameter  
             K   beam       m   eff         ;       
 
 the value of this determines the cutoff frequency f for impact noise, accordingly the spring rate K beam  and effective mass m eff  are determined to be at or below this cutoff frequency f. This actuator with a spring like cushioned surface contacting portion dramatically reduces rattle noises above the cutoff frequency, f which can be as low as the designer wishes however is typically kept above 300 Hz.
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a side view of the inventive seatbelt retractor, showing a first embodiment inertial sensor mass, actuator and seatbelt retractor in an unlocked position.  
         [0013]      FIG. 2  is a side view of the inventive seatbelt retractor, showing a first embodiment inertial sensor mass, actuator and seatbelt retractor in a locked position.  
         [0014]      FIG. 3  outlines the engineering parameters in designing the actuator.  
         [0015]      FIG. 3A  illustrates the actuator of the present invention and the relationship between F static  and m eff .  
         [0016]      FIG. 4  is a schematic spring mass.  
         [0017]      FIG. 5  illustrates a perspective view of the actuator.  
         [0018]      FIG. 6  illustrates a second embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]      FIG. 1  is a side view of an inventive seatbelt retractor assembly  10 . The seatbelt retractor assembly  10  has a seatbelt retractor  14 , which houses a seatbelt  18  as shown. Like conventional seatbelt retractors, the seatbelt retractor assembly  10  has a locking pawl  22 , which is selectively engageable with a locking wheel  28 . The locking wheel  28  has teeth to engage the locking pawl  22 . When the locking pawl  22  is engaged with the locking wheel  22 , the seatbelt retractor  14  prevents the seatbelt  18  from extending further from seatbelt retractor  14 .  
         [0020]     As shown, the seatbelt retractor  14  has an inertial sensor, here an inertial sensor mass  30 , which is responsive to vehicle acceleration. The inertial sensor mass  30  rests on a sensor housing  24 , here shown schematically, and tips in the direction of either arrow P or arrow Q in response to vehicle acceleration. The inertial sensor mass  30  is linked to the locking pawl  22  by an actuator  26 , an arm, which causes the locking pawl  22  to engage or disengage the locking wheel  28  depending upon the position of the inertial sensor mass  30 . While the locking pawl  22  is shown schematically as a separate component from the actuator  26 , the locking pawl  22  and actuator  26  may, in fact, be a single part. As shown in  FIGS. 1 and 2 , the actuator  26  interacts with a guide surface  34  through an actuator surface contacting portion  54 . The actuator surface contacting portion  54  has an actuator curvature  58 . The actuator curvature  58  as illustrated is generally a hemispherical surface or approximates a rounded protruding bottom which directly contacts the guide surface  34 . At the near zero vehicle acceleration the actuator  26  contacts the guide surface  34  at the contact point  100 . An open slot  57  is shown above the surface contacting portion  54  and a beam structure  56  as shown.  
         [0021]      FIG. 1  illustrates the inertial sensor mass  30  in an unlocking position. When in this position, the actuator  26  maintains the locking pawl  22  in an unlocked condition, allowing the seatbelt  18  to be withdrawn from the seatbelt retractor  14 . The actuator  26  is pivotally mounted by a pivot  19  so as to rotate in the direction of arrow R in response to movement of the inertial sensor mass  30  in the direction of arrow P or in the direction of arrow Q. In the event of a quick acceleration or deceleration of a vehicle, such as in a crash, the inertial sensor mass  30  responds by moving either in the direction of arrow P or in the direction of arrow Q. In either direction, the actuator  26  moves in the direction of arrow R.  
         [0022]     As shown in  FIG. 2 , the inertial sensor mass  30  is shown having moved in the direction of arrow P from the unlocking position  38  shown in  FIG. 1  to a locking position  42 . Movement of the inertial sensor mass  30  has caused the actuator  26  to move in the direction of arrow R from the position shown in  FIG. 1 . This movement of the actuator  26  causes the locking pawl  22  to engage the teeth of the locking wheel  28 . The return movement of the inertial sensor mass  30  in the direction of arrow Q towards the unlocking position  38  causes a return of the actuator  26  in the direction of arrow S to the position shown in  FIG. 1 .  
         [0023]     The first embodiment of the invention will now be explained in detail with reference to  FIG. 1 . As shown in  FIG. 1 , the guide surface  34  is located on a wide portion  46  above a narrow portion  50 . While the figures show a particular shape of an exemplary sensor mass  30  upon which guide surface  34  sits, guide surface  34  may be implemented as any shape such as a sphere or cone shape. Under small amplitude vibration loading, actuator  26  can occasionally “jump” in direction R, momentarily losing contact between guide surface  34  and surface contacting portion  54 . When actuator  26  rebounds back in direction S, contact will be re-established. Such intermittent contact can produce an audible rattle noise, which this invention seeks to eliminate. Beam structure  56  reduces the rattle noise by softening the contact between actuator  26  and guide surface  34 . If beam structure  56  is made to be softer, the intermittent contact noise becomes quieter. If beam structure  56  is made to be stiffer, the intermittent contact noise becomes louder. If open slot  57  is removed completely, (i.e. in the absence of this invention) then there is no cushion at all and the intermittent contact noise would be as loud as possible. Open slot  57  is sized to be large enough that deflections of beam structure  56  due to vehicle vibrations will be unimpeded. Under higher loads, however, such as may occur during a rapid change in vehicle speed, open slot  57  is small enough to restrict beam structure  56  so that rapid locking can still occur with the sensor mass  30  tilting in the direction P or Q as shown in  FIG. 2 .  
         [0024]     With reference to  FIGS. 3, 3A  and  4 , the underlying principle of the invention can best be understood by using a spring-mass analogy. In other words the open slot  57  provides space for a limited amount of deflection of the actuator surface contacting portion  54  and the beam structure  56  relative to the actuator arm  25  of the actuator  26 .  
         [0025]     As shown in  FIG. 3  the surface contacting portion  54  has a force F applied tending to put a load on the beam structure  56  to deflect it in the direction X. This load can be due to the static weight of the actuator  26  and it can also be due to impacts between the actuator  26  and the sensor  30 .  
         [0026]     Using classical beam theory, an idealized beam stiffness can be computed as follows: The beam structure as found in  Marks&#39; Standard Handbook of Mechanical Engineering,  10 th  edition, has a thickness (c) and a width (b) and a length (l). Accordingly the beam structure acts like a leaf spring wherein the spring rate or spring constant  
         K   beam     =       F   X     =       3   ⁢     EI     l   3         =       Eb   4     ⁢       (     c   l     )     3               
 
 where E is the modulus of the actuator material. If the beam is more complicated than  FIG. 3 , then other analysis would be required, and this is understood by one of ordinary skill in the art. 
 
         [0027]      FIG. 3A  shows a Free Body Diagram associated with the actuator  26 . Considering the sum of the torques about the pivot  19 , it is seen that the actuator contact force, F static , must equal m eff *g where m eff  is the equivalent mass of actuator  26  if the CG (center of gravity) of the actuator  26  were placed directly over the actuator contact point  100 ; thus m eff =F static /g.  
         [0028]      FIG. 4  shows an idealized spring-mass system analogous to the invention. An equivalent mass, m eff  is supported by a spring whose spring rate is K beam . This is equivalent to the actuator of  FIG. 5  where the effective mass of the actuator  26  is supported by beam structure  56 . This means that the oscillation frequency (f) of the actuator  26  can be assumed to meet the equation  
         f   =       1     2   ⁢   π       ⁢         K   beam       m   eff             ;           ⁢     or   ⁢           ⁢     1     4   ⁢   π       ⁢       Eb     m   eff         ⁢       (     c   l     )     3             
 Note that the beam structure  56  can have more complicated geometry in which case more sophisticated analysis is required to compute the oscillation frequency f. Symbol F refers to a force and f to a frequency. The ratio of effective mass to contact stiffness indicates contact sharpness or impact stiffness. Accordingly the spring effect of the open slot  57  and beam structure  56  acts much like a low pass filter, wherein noise reduction were observed wherein (f)=300 Hz, (more typically (f) will be greater than 300 Hz generally 1000 Hz-1500 Hz however (f) can be designed to be as high as 20,000 Hz—the upper frequency limit of human hearing—and still have some remaining benefit). These noise reductions can be easily accomplished by adjusting the open slot length defining the beam length (l), the beam thickness (c) or beam width (b). In other words the geometry of the beam structure  56  can be adjusted to change the overall spring rate up or down as required to achieve the desired oscillator frequency to achieve a reduction in actuator rattle noise. 
 
         [0029]     With reference to  FIG. 5 , the actuator  26  is shown in a perspective view showing the actuator arm  25 , the pivot axis  19 , the open slot  57  with the surface contacting portion  54  and beam structure  56 . As shown the actuator can be formed as unitary single piece structure by injection molding a plastic material. Preferably the actuator is made of acetyl, polypropylene, nylon or polyethylene or similar light weight easily molded material. The choice of materials could be almost any material including steel and aluminum as long as the desired spring like cushioning effect is achieved to reduce the contact noise.  
         [0030]     While the open slot  57  is shown as a straight grooved opening in the actuator it is understood the shape of the opening can be varied to any variety of openings including wavy, triangular or curved with the resultant underlying beam structure optionally having an adjacent corresponding shape. The important aspect is that the open slot  57  provides a cushioning effect by providing a spring like beam structure  56  capable of minute deflections under normal vibrational inputs from a moving vehicle. Under an acceleration sufficient to create a locking of the seatbelt retractor the gap in the actuator  26  at the open slot  57  will close or otherwise be sufficiently small as to allow timely locking of the device. This also creates a lower impact noise as the actuator  26  moves to a locking engagement as shown in  FIG. 2 .  
         [0031]     As used herein the term open slot  57  refers to a void volume. In the embodiment described in  FIGS. 1 and 5  the open slot  57  was located directly above the surface contacting portion  54  and extending inwardly above the beam structure  56 , the open slot  57  providing a gap sufficient to allow a flexure of the portions  54  and  56  and being completely open across the entire width of the surface contacting portion  54  and beam structure  56  during normal driving conditions.  
         [0032]     While the open slot  57  is shown generally extending horizontally it is understood the open slot can be inclined or even bent extending above the surface contacting portion  54  into the actuator arm  25  to define a beam structure  56  of any desired geometric shape. Additionally, open slot  57  may have more complicated geometry such as a sawtooth pattern, for example. One skilled in the art will realize the usefulness of a nonplanar open slot.  
         [0033]     With reference to  FIG. 6 a  second embodiment of the invention is shown wherein the actuator  26  has an open slot  57  that extends substantially vertically with an optional short enlarged end  59  such that the beam structure  56  as shown forms a relatively thin hinge which can reduce the impact noise upon locking into the lock position  42  as well as providing a spring like effect during normal driving conditions.  
         [0034]     Preferably the open slot  57  is at least partially closed in the locked position and the flexibility of the beam structure  56  is sufficient to provide a noise reduction under normal driving condition use as well. As shown the open slot  57 ,  59  is above the surface contacting portion  54  but offset or located inwardly and extending generally vertically cutting across the width of the actuator arm  25 .  
         [0035]     The aforementioned description is exemplary rather that limiting. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed. However, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. Hence, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For this reason the following claims should be studied to determine the true scope and content of this invention.