Abstract:
A variable load limiting restraint retractor for a seat restraint system in a vehicle includes a housing for operative connection to vehicle structure. The variable load limiting restraint retractor also includes a take-up spool operatively connected to the housing and connected to a belt of a seat restraint system for winding and unwinding the belt. The variable load limiting restraint retractor includes a rotatable shaft operatively connected to the take-up spool and the housing, the take-up spool being mounted on the shaft. The variable load limiting restraint retractor further includes a load limiting assembly operatively connected to the shaft for variably limiting load on the belt when the seat restraint system is in a buckled position.

Description:
TECHNICAL FIELD 
     The present invention relates generally to seat restraint systems for vehicles and, more particularly, to a variable load limiting restraint retractor for a seat restraint system in a vehicle. 
     BACKGROUND OF THE INVENTION 
     It is known to provide a seat restraint system such as a seat belt in a vehicle to restrain an occupant in a seat of the vehicle. In some vehicles, the seat restraint system may be a lap belt, a shoulder belt or both. Typically, the lap belt and shoulder belt are connected together at one end. The seat restraint system includes a latch plate at the connected end. The seat restraint system also includes a buckle connected at one end by webbing or the like to vehicle structure. The buckle receives the latch plate to be buckled together. When the buckle and latch plate are buckled together, the seat restraint system restrains movement of the occupant to help protect the occupant during a collision. 
     It is also known to provide a restraint retractor for the seat restraint system. Typically, the restraint retractor has a spool attached to belt webbing of the seat restraint system and is rotatably mounted to the restraint retractor by a shaft. The restraint retractor has a spiral spring on one end of the shaft to urge the spool in a direction for retracting the belt webbing when not in use. Also, the restraint retractor has a toothed locking sprocket on the other end of the shaft and a locking pawl to engage the sprocket to lock the shaft against rotation in the other direction to prevent belt webbing unwinding. The locking sprocket is typically slaved to an acceleration sprocket via a spring and an acceleration pawl is actuated by an acceleration sensing mechanism or sensor. The acceleration sensor includes a mass member or “standing man” that may be spherically shaped or frusto-conical in shape to engage and actuate the acceleration pawl. 
     The restraint retractor includes a load limiter such as a torque rod providing single (constant) level load limiting. Load leveling means that the restraint retractor will allow controlled belt webbing unwinding or payout. Some attempts have been made to provide a dual load limiter through the use of a torque rod, which only has two settings. Therefore, it is desirable to provide a multiple level or variable load limiting restraint retractor for a seat restraint system in a vehicle. It is also desirable to provide a restraint retractor for a seat restraint system in a vehicle that uses a magnetorheological fluid to provide a variable load limiting effect and, in some cases, a primary locking mechanism for the restraint retractor. It is further desirable to provide a variable load limiting restraint retractor for a seat restraint system in a vehicle that has infinite settings and reduced cost. 
     SUMMARY OF THE INVENTION 
     It is, therefore, one object of the present invention to provide a variable load limiting restraint retractor for a seat restraint system in a vehicle. 
     It is another object of the present invention to provide a variable load limiting restraint retractor for a seat restraint system in a vehicle that uses a magnetorheological fluid. 
     To achieve the foregoing objects, the present invention is a variable load limiting restraint retractor for a seat restraint system including a housing for operative connection to vehicle structure. The variable load limiting restraint retractor also includes a take-up spool operatively connected to the housing and connected to a belt of a seat restraint system for winding and unwinding the belt. The variable load limiting restraint retractor includes a rotatable shaft operatively connected to the take-up spool and the housing, the take-up spool being mounted on the shaft. The variable load limiting restraint retractor further includes a load limiting assembly operatively connected to the shaft for variably limiting load on the belt when the seat restraint system is in a buckled position. 
     One advantage of the present invention is that a variable load limiting restraint retractor is provided for a seat restraint system in a vehicle. Another advantage of the present invention is that the variable load limiting restraint retractor uses a magnetorheological fluid to provide multiple or infinite levels of load limiting, which allows for tailoring the load limit or restraint for each occupant, occupant weight and vehicle speed. Yet another advantage of the present invention is that the variable load limiting restraint retractor may provide the primary locking means for a restraint retractor, thus eliminating mechanical components now used to sense and lock the restraint retractor. Still another advantage of the present invention is that the variable load limiting restraint retractor reduces cost by eliminating mechanical components used for the primary locking mechanism, and improve quality by noise reduction due to limited mechanical components. 
    
    
     Other objects, features and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a variable load limiting restraint retractor, according to the present invention, illustrated in operational relationship with a seat restraint system of a vehicle. 
     FIG. 2 is a perspective view of the variable load limiting restraint retractor of the seat restraint system of FIG.  1 . 
     FIG. 2A is a partial fragmentary elevational view of a portion of the variable load limiting restraint retractor of FIG.  2 . 
     FIG. 3 is an exploded view of another portion of the variable load limiting restraint retractor of FIG.  2 . 
     FIG. 4 is a fragmentary elevational view of the portion of the variable load limiting restraint retractor of FIG. 3 illustrating a first operational state. 
     FIG. 5 is a view similar to FIG. 4 illustrating a second operational state of the variable load limiting restraint retractor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings and in particular FIGS. 1 and 2, one embodiment of variable load limiting restraint retractor  10 , according to the present invention, is shown for a seat restraint system, generally indicated at  12 , in a vehicle (partially shown), generally indicated at  14 . The vehicle  14  includes a vehicle body  16  and a seat  18  mounted by suitable means to vehicle structure  20  such as a floorpan in an occupant compartment  22  of the vehicle body  16 . In this embodiment, the seat  18  is a front seat of the vehicle  14 . It should be appreciated that the seat  18  could be a rear, second row or third row seat for the vehicle  14 . 
     The vehicle  14  includes the seat restraint system  12  for restraining an occupant (not shown) in the seat  18 . The seat restraint system  12  includes a latch tongue or plate (not shown) connected to an end of either one of a lap belt (not shown), shoulder belt  24 , or both which have another end connected to the variable load limiting restraint retractor  10  to be described. The seat restraint system  12  also includes a buckle assembly (not shown) connected by suitable means such as belt webbing (not shown) to the vehicle structure  20 . The latch plate is engageable and disengageable with the buckle assembly as is known in the art. It should be appreciated that, except for the variable load limiting restraint retractor  10 , the seat restraint system  12  and vehicle  14  are conventional and known in the art. 
     Referring to FIGS. 2,  2 A and  3 , the seat restraint system  12  includes the variable load limiting restraint retractor  10  connected to either the lap belt or the shoulder belt  24 . In the embodiment illustrated, the variable load limiting restraint retractor  10  is connected to the shoulder belt  24 . The variable load limiting restraint retractor  10  includes a housing  26  having a base wall  28  and spaced apart sidewalls  30 . The variable load limiting restraint retractor  10  also includes a belt reel or take-up spool  32  disposed between the sidewalls  30  and connected by suitable means to the end of the shoulder belt  24 . The variable load limiting restraint retractor  10  also includes a shaft  34  extending through the take-up spool  32  and the sidewalls  30  of the housing  26  such that the take-up spool  32  is rotatable relative to the housing  26 . It should be appreciated that the housing  26  is attached by suitable means (not shown) to vehicle structure. 
     The variable load limiting restraint retractor  10  also includes a retractor spring  36  disposed about one end of the shaft  34 . The retractor spring  36  is of a spiral type having one end attached to the shaft  34  and another end connected to the housing  26  as known in the art. The retractor spring  36  may be enclosed by a spring housing  37  attached to the sidewall  30  of the housing  26 . The retractor spring  36  has a predetermined torque or tension and urges the shaft  34  in a predetermined direction to wind up the shoulder belt  24  on the take-up spool  32 . It should be appreciated that the variable load limiting restraint retractor  10  may have a structure similar to that disclosed in U.S. Pat. No. 4,815,674 to Blake et al. 
     Referring to FIGS. 2 through 4, the variable load limiting restraint retractor  10  also includes a load limiting assembly, generally indicated at  38  attached to the other end of the shaft  34  opposite the spring  36  to allow controlled belt webbing unwinding or payout of the shoulder belt  24 . The load limiting assembly  38  includes has a housing  40  extending axially. The housing  40  is generally rectangular in shape, but may have any suitable shape. The housing  40  has a cavity  42  in one axial end and a passageway  43  extending axially through the other axial end and communicating with the cavity  42 . The cavity  42  and passageway  43  each have a generally circular cross-sectional shape, but may be any suitable shape. The housing  40  also has an annular groove  43   a  disposed about the passageway  43 . The housing  40  is made of a rigid material such as metal, preferably steel. 
     The load limiting assembly  38  also includes piston  44  disposed in the housing  40 . The piston  44  has a piston portion  46  extending radially and a shaft portion  48  extending axially. The piston portion  46  is generally circular in shape and located axially between the ends of the shaft portion  48 . The piston portion  46  is disposed in the cavity  42  of the housing  40  and terminates prior to the wall of the cavity  42  to form a gap or space  50  therebetween for a function to be described. The piston portion  46  also includes an annular groove  52  extending radially inward from an outer periphery thereof for a function to be described. The shaft portion  48  extends axially through the passageway  43  of the housing  40 . The outer surface of the shaft portion  48  has a plurality of flats  53  to form a generally hexagonal shape for a function to be described. The shaft portion  48  has a cavity  54  in one axial end and an aperture  56  extending axially from the other axial end and communicating with the cavity  54 . The aperture  56  has a plurality of threads  58  for threadably engaging a plurality of threads  60  on one end of the shaft  34 . A seal  57  is disposed in the groove  43   a  of the housing  40  and contacts the shaft portion  48 . The piston  44  is made of rigid material such as metal, preferably steel. It should be appreciated that the piston  44  is a monolithic structure being integral, unitary and one-piece. 
     The load limiting assembly  38  also includes a nut plate  62  disposed between the housing  40  and sidewall  30  to prevent rotational movement of the piston  44 . The nut plate  62  is generally rectangular in shape and has an aperture  64  extending therethrough. The aperture  64  has a generally hexagonal shape to receive the hexagonal shape of the shaft portion  48 . The nut plate  62  also includes a plurality of recesses  66  at the corners thereof to receive the legs of the housing  40 . The recesses  66  cooperate with the legs to prevent the nut plate  62  from rotating relative to the housing  40 . The nut plate  62  is made of a rigid material such as metal, preferably steel. 
     The load limiting assembly  38  includes a spring  68  disposed between the nut plate  62  and the sidewall  30  to urge the nut plate  62  against the housing  40 . The spring  68  is of a leaf or wave type and formed as a ring to allow the shaft  34  to pass therethrough. 
     The load limiting assembly  38  also includes a seal  70  disposed in the cavity  42  of the housing  40  and about the other end of the shaft portion  48 . The seal  70  is generally circular in shape and has an aperture  72  extending therethrough. The aperture  72  is generally circular in shape and receives the shaft portion  48 . The seal  70  also has an annular inner groove  74  extending radially and circumferentially from the aperture  72 . The seal  70  also has an annular outer groove  76  extending radially and circumferentially from the outer periphery thereof. The seal  70  has an inner seal ring  78  disposed in the inner groove  74  to engage the shaft portion  48  and an outer seal ring  80  disposed in the outer groove  76  to engage the wall of the cavity  42 . The seal rings  78  and  80  are made of a flexible material such as an elastomeric material. It should be appreciated that the seal  70  forms a chamber  82  in the cavity  42  between the housing  40  and the seal  70  for a function to be described. 
     The load limiting assembly  38  includes a fluid  84  disposed in the chamber  82 . The fluid  84  is of a magnetorheological (MR) type having a suspension of fine, for example in a range of 1 to 50 microns, magnetizable solid in a fluid carrier medium. The MR fluid has a shear stress controlled by an applied magnetic field in which in off state has laminar flow (parabolic velocity profile) and in an ON state has a shear stress greater than a yield stress. Alternatively, the fluid  84  may be of an electro-rheological (ER) type. It should be appreciated that the shear stress of the MR fluid is controlled by an applied magnetic field. It should also be appreciated that such MR fluids and ER fluids are conventional and known. 
     The load limiting assembly  38  also includes an electrical coil  86  disposed in the groove  52  of the piston  44  to provide the applied magnetic field. The coil  86  is connected to a source of power (not shown) such as an electronic controller of the vehicle. It should be appreciated that the power through the coil  86  creates magnetic flux, which travels through the housing  40  and fluid  84 . It should be appreciated that the housing  40  may be made as the coil  86  and the piston  44  made of steel. 
     The load limiting assembly  38  further includes a cover  88  to cover the end of the cavity  42 . The cover  88  is generally rectangular in shape and abuts the end of the housing  40 . The cover  88  includes a plurality of apertures  90  extending axially therethrough and disposed near the corners thereof. The cover  88  is made of a rigid material such as metal, preferably steel. The load limiting assembly  38  also includes a plurality of fasteners  92  such as screws extending through the apertures  90  and apertures  94  in the housing  40  and threadably engage apertures  96  in the sidewall  30  to secure the load limiting assembly  38  to the housing  26 . 
     In operation of the variable load limiting restraint retractor  10 , an occupant (not shown) grasps the latch plate and pulls on the lap belt and shoulder belt  24 . The shoulder belt  24  is unwound by the occupant from the spool  32  of the variable load limiting restraint retractor  10 . The occupant engages the latch plate with the buckle assembly to restrain the occupant in the seat  18 . When an impact of the vehicle is sensed, power is sent to the coil  86  to apply a magnetic field to the fluid  84 , thereby changing its characteristics. As belt webbing is payed-out due to a load on the shoulder belt  24  by the occupant, the shaft  34 , which is connected to the spool  32 , is rotated. As the shaft  34  rotates, the piston  44  is locked against rotation by the nut plate  62  and translates axially due to the interaction between the threads  58 , 60 . As the piston  44  translates, the piston portion  46  causes the fluid  84  in a first sub-chamber of the chamber  82  to flow around the piston portion  46  through the gap  50  to a second sub-chamber of the chamber  82  on the other side of the piston  44 . It should be appreciated that, when energized, the coil  86  creates a magnetic field, which changes the viscosity of the fluid  84 , thus creating resistance to motion and controlled belt payout of the shoulder belt  24 . It should also be appreciated that the piston  44  moves in a linear manner. It should further be appreciated that operation is reversible very quickly. 
     The variable load limiting restraint retractor  10  provides variable load limiting by setting the amount of load limiting as a function of the input current profile to the coil  86  as controlled by the electronic controller. Since the fluid viscosity changes with respect to current, the amount of load limiting can be tailored for occupant type and/or vehicle impact. The variable load limiting restraint retractor  10  has a millisecond response time and provides controllable damping and/or clutching. The variable load limiting restraint retractor  10  may replace mechanical locking by placing the load limiting assembly  38  on both sides of the retractor. It should be appreciated that, when the coil  86  is not energized, the variable load limiting restraint retractor  10  functions similar to a conventional retractor to pull in the shoulder belt  24 . It should also be appreciated that the load limiting assembly  38  may be configured to be placed inside the spool  32 . 
     The present invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. 
     Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced other than as specifically described.