ENERGY ABSORBING SEAT BELT RETRACTOR

Abstract: A seat belt retractor (50) has a spool (56) about which a seat belt is wound. A locking mechanism (60) at least initially locks the spool against rotation. A primary force-limiting mechanism, such as a torsion bar (58), permits the spool to rotate in a controlled manner subsequent to the locking of the spool. A secondary force-limiting mechanism is located within a recess (100) in the spool and comprises portions of the spool and an adjacent portion of the locking mechanism to increase the restraining force on the seat belt before the primary force-limiting mechanism becomes effective. The torsion bar (58) is connected at one end to the spool and at its other end to the locking mechanism. The secondary locking mechanism includes a recess, keyway or slot (102) and a projection (104) formed on one of the bore and an interlocking part of the locking mechanism.

Description: ENERGY ABSORBING SEAT BELT RETRACTOR The invention generally relates to seat belt retractors and more particularly to that class of seat belt retractors having an energy absorbing mechanism. A seat belt retractor with an energy absorbing mechanism permits the seat belt to be controllably protracted from the retractor spool as a mechanism within the spool generates a determinable, somewhat level or constant, reaction force or torque to oppose the protraction. This action permits the vehicle occupant to move forwardly during a crash and lessens the crash forces exerted on the vehicle occupant. US 6 105 894 suggests the use of an additional energy- absorbing element such as shear pins, which extend from an end face of a spool flange and connect the spool to the locking mechanism. These pins must first be shorn off in order to permit the torsion bar to work. The physical characteristics of the shear pins increase the force or torque applied to the vehicle occupant and introduce a peak in the force curve that corresponds to the force or energy needed to break or shear the shear pins . After the pins have been shorn off, the torsion bar is permitted to twist, generating the more constant value of reactive force dictated by the characteristics of the particular torsion bar or other type of energy- absorbing mechanism used. One of the deficiencies of this prior art retractor is that the shear pin acts as a rivet to hold the lock mechanism to the spool and once this rivet or shear pin is torn off, the retractor loses its functionality. Additionally, in the prior design, it may be possible for a sheared or broken-off piece of the pin to lodge itself in a position within the retractor to jam the retractor. A seat belt retractor according to the present invention comprises: a spool about which a seat belt is wound; a locking mechanism at least initially locking the spool against rotation and a primary force-limiting mechanism, such as a torsion bar for permitting the spool to rotate in a controlled manner subsequent to the locking of the spool and a secondary force-limiting mechanism located within a recess of the spool and comprised from portions of the spool and an adjacent portion of the locking mechanism for increasing the restraining force on the seat belt before the primary force-limiting mechanism becomes effective. The' torsion bar is at least partially located within a spool bore and is connected at one end to the spool and at its other end to the locking mechanism. The secondary locking mechanism includes a recess, keyway or slot and a projecting, breakable tab formed on one of a spool bore and an interlocking part of the locking mechanism. Brief Description of the Drawings Fig. 1 is a cross-sectional view showing the major components of a seat belt retractor incorporating the present invention. Fig. 2a is an end view of part of a locking mechanism. Fig. 2b is a side view of part of the locking mechanism. Fig. 2c is a cross-sectional view showing an alternate embodiment of the invention in which the placement of slots and pins are reverse. Figs. 3a, 3b and 3c show a cross-sectional, end plan and side plan view of a spool. Fig. 4 is an assembly view showing an isometric view of the spool and locking mechanism (the lock wheel is not shown) . Fig. 5 shows various force/time (deflection) curves . Detailed Description of the Invention Figs. 1-4 illustrate the major components of a seat belt retractor incorporating the present invention. The seat belt retractor 50 comprises a U- shaped frame 52 having openings 52a, 52b to support a spool and locking sub-assembly 54. These openings act as bearings. The spool and locking sub-assembly comprises a spool 56, a torsion bar 58, and a lock mechanism 60. One end 62 of the torsion bar 58 includes a plurality of splines 64, which drivingly engage a mating plurality of splines 66 formed on the torsion bar (in a known manner) . An extension 68 of the torsion bar is received into a spring arbor 70 and biased by a rewind spring 72. The other end 74 of the reaction of the torsion bar 58 is secured to the lock wheel mechanism 60. The mechanism 60 includes a splined bore 80, which receives splines 82 formed on end 74 of the torsion bar. This rotationally connects the torsion bar and the lock mechanism 60. The lock mechanism and torsion bar are axially fixed by swaging these parts together. The torsion bar 68 further includes an additional extension 84, which rotates with the spool prior to activation of the torsion bar and serves as part of a known type of web sensor 86 that is schematically indicated. The lock mechanism 60 includes a ratchet wheel 86, which forms a cavity 88. The various parts of the web sensor, such as a web sensor pawl, are located within the cavity 88 (also shown in Fig. 4) formed by the ratchet wheel. Secured to the body 90 of the lock mechanism is a lock wheel 92 having a plurality of teeth 94. A lock pawl 96, shown schematically, is rotationally mounted to the frame and is brought into engagement with one or more teeth 94, of the low wheel, upon operation of the web sensor or vehicle sensor 98 in a known manner. As is known in the art, many seat belt retractors include a lock ring (not shown) that is rotatable relative to the retractor's shaft (in this case, the torsion bar) ; the activation of the web sensor or of a cooperating vehicle sensor connects this lock ring to the retractor shaft. This action causes the lock ring to rotate a small amount and in so doing moves the lock pawl into engagement with the lock wheel. The web sensor includes an inertia disk loosely mounted to the extension 84 and a web sensor pawl (not shown) rotatably mounted to a pin 87 of the ratchet wheel 86, which in response to rapid protraction of the seat belt from the retractor spool moves to engage closely spaced teeth on the lock ring, thereby coupling the lock ring to the pawl and to the retractor shaft. The vehicle sensor 98, which can be carried by the lock ring, also includes a vehicle sensor pawl 98a, which is moved to an activated position by a movable mass (not shown) when the vehicle experiences a rapid deceleration. In the activated position the vehicle sensor pawl 98a engages the teeth 86a of the ratchet wheel 86, thereby coupling the lock ring to the retractor shaft. Fig. 4 shows that the central bore 100 of the spool 56 includes at least one slot (also referred to as a keyway) 102. The body 90 of mechanism 60 includes a plurality of projections 104 that are received within the keyways 102. The projections 104 and keyways 102 drivingly connect the interior of the spool to the exterior of the body 90 of the mechanism 60. The body 90 includes a narrow diameter portion 90a that is received within the bore 100 of the spool and a larger diameter portion 90b that is received within and stabilized by opening, i.e. bearing, 52b in the frame. In the embodiment illustrated, the spool also includes two bores 110 that are perpendicular to bore 100. With the torsion bar 58 in place as illustrated in Fig. 2, a tool is positioned within bores 110 and, with the application of force, locally deforms the spool so that the splines 66 of the spool remain in driving contact with the splines 64 of the torsion bar. Other means can be used to secure the torsion bar to the spool. The spool 56 further includes a provision to receive an end of a seat belt 130. Such provision includes a known slot 132 into which an end of the belt 130 is received. Retention may be enhanced by first securing the end of the belt about a pin that fits within the slot 132. The belt is wound about the spool body 134 and retained between optional flanges 136a, 136b. During a crash the vehicle and/or web sensor connect the lock ring (not shown) to the shaft (torsion bar) which causes the lock ring to rotate a small amount. A part of the lock ring is operatively connected to the lock pawl 96 and the rotation of the lock ring moves the lock pawl 96 into engagement with the teeth 94 of the lock wheel 92, thereby at least initially, prohibiting seat belt webbing from protracting from the spool 56. As the crash progresses, crash forces are exerted on the seat belt by the vehicle occupant, tending to try to pull the seat belt in the direction of arrow F (see Fig. 1) off from the spool 56. This force is resisted by the locking pawl and lock teeth 94 interaction, as well as by the interaction between the projections 102 and the slots 104. As the level of crash forces increase to a level sufficient to cause the projections 102 to shear from the body 90a of the lock mechanism 60, a reaction force such as a reaction force of magnitude 202 is generated as shown in Fig. 5. Because of the higher reaction forces, indicated by numeral 202a in Fig. 5, generated by the slots and the pins, the vehicle occupant's forward motion will be forcefully opposed and the vehicle occupant's motion restricted. When the projections 104 are shorn off they will become lodged within a corresponding keyway, and the spool and torsion bar are free to rotate relative to the lock mechanism as continued vehicle occupant-generated forces are input to the seat belt and then to the spool. As can be appreciated, it is end 62 of the torsion bar that begins to twist as end 74 is held fixed to the non-rotating lock mechanism 60, which is held by the lock pawl. As the torsion bar rotates, it will generate a lesser reaction force 202a, as also shown in Fig. 5, which will resist the forward motion of the vehicle occupant, however, this level of force will permit the vehicle occupant to move forwardly such that the crash forces acting on the vehicle occupant are now limited based upon the characteristics of the torsion bar. As can be appreciated, one of the benefits of this type of design is that the sheared-off projections 104 are encapsulated within the spool and will not impede the functionality of the spool. The traces in Fig. 1 show test data and more particularly belt force and a function of time (which is illustrative of belt protraction) . Trace 200 shows comparative test data for a similar seat belt retractor that does not include the slots and pins. Fig. 2c shows an embodiment in which the slots are formed in the lock mechanism and the shear pins are incorporated into the spool.

Claims: Claims seat belt retractor (50) comprising: spool (56) about which a seat belt is wound; locking mechanism (60) at least initially locking the spool against rotation and a primary force-limiting mechanism (58) for permitting the spool to rotate in a controlled manner subsequent to the locking of the spool and secondary force-limiting mechanism located within a recess (100) in the spool (56) and comprising portions of the spool and an adjacent portion of the locking mechanism for increasing the restraining force on the seat belt before the primary force-limiting mechanism (58) becomes effective. 2. he seat belt retractor (50) defined in Claim 1 wherein the recess of the spool (56) includes a part of a bore and wherein the secondary force- limiting mechanism includes a slot or keyway (102) and a projection (104) formed on one of the bore and an interlocking part of the locking mechanism (60) . 3. he seat belt retractor (50) defined in Claim 2 wherein the primary force-limiting device (58) is a torsion bar having one end connected to the spool (56) and another end connected to the locking mechanism (60) . 4. he seat belt retractor (50) defined in Claim 1 wherein the secondary force-limiting mechanism includes opposing slots (102) and breakable projections (104) .

Inventors: KONING RICHARD W, W LLARD SCOTT A, KONING, RICHARD, W., W0LLARD, SCOTT, A.
Applicants: BREED AUTOMOTIVE TECH, BREED AUTOMOTIVE TECHNOLOGY, INC.
Application year: 2001
Main classification: B60R22
IPC codes: A44B11, B60R22