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SEATBELT RETRACTOR WITH TORSION BAR

This invention relates to seatbelt retractors with load limiting torsion bars.

In a crash a seatbelt retractor has a lock that limits the extension of the seatbelt from the housing. In a locked condition a conventional seatbelt system restrains the vehicle occupant from moving forward. Although the seatbelt has some give, the restraining force on the vehicle occupant can be significant. To reduce this force manufacturers may use a torsion bar to absorb energy from the forward movement of the vehicle occupant in a controlled manner. The torsion bar twists and deforms as the seatbelt is protracted such that the vehicle occupant is stopped more gradually during the crash.

Heavier vehicle occupants require a greater restraining force than lighter vehicle occupants. It is desirable to use a higher rate of energy absorption for a heavy vehicle occupant than for a lightweight vehicle occupant.

Recently manufacturers began producing seatbelt retractors that absorb energy at different rates to accommodate differently weighing vehicle occupants. For example, when a small person is seated in the vehicle, the seatbelt retractor is set at a low rate of energy absorption such that the lighter weighing vehicle occupant is restrained with less restraining force than a heavier vehicle occupant. On the other hand, for a heavier vehicle occupant, a higher energy absorption rate is used to slow the heavier vehicle occupant with greater restraining force. A middleweight vehicle occupant may require a combination of restraining force rates during a crash. In this way a vehicle occupant receives a restraining force that better accommodates his weight.

In some situations a vehicle experiences successive crashes. It is desirable to continue to absorb energy at the same high rate for the heavy vehicle occupant in a second crash. However, for a lightweight vehicle occupant, it is preferable to absorb energy from the seatbelt spool initially at

a low rate for the first crash, then at the higher rate for the second crash. Moreover, for a middleweight vehicle occupant, it is desirable to absorb energy at a high rate and then a low rate for the initial crash. For the second crash, a high rate of energy absorption is preferred. Conventional seatbelt retractors do not have such a feature. A need therefore exists for a multilevel energy absorbing retractor that solves the foregoing problem.

The present invention provides a solution to this problem through an outer sheath that is cast, molded, coated or otherwise bonded to and encircling a portion of an external surface of the first portion of the torsion bar which upon a sufficient exposure to rotational energy breaks a bond between the first portion and the outer sheath.

Figure 1 is a perspective cross-section of the new seatbelt retractor.

Figure 2 is a cross-section of the shift mechanism of the seat belt retractor of Figure 1.

Figure 3 is a cross-section of the seatbelt retractor of Figures 1 and2.

Figure 4 is a cross-section of the seatbelt retractor of Figures 1 - 3.

Figure 5 is a perspective view of the seatbelt retractor of Figures 1-4.

Figure 6 shows the coupler of in an actuated condition.

Figure 7 is an exploded view of the seatbelt retractor.

Figure 8 is a perspective cross-section of the seatbelt retractor with an improved torsion bar.

Figure 9 is a cross-section of the shift mechanism of Figure 8, showing the torsion bar set at a high rate of energy absorption.

Figure 10 shows seatbelt retractor of Figures 8-9 with the torsion bar set at a relatively low rate of energy absorption.

Figure 11 is a cross-section of the seatbelt retractor of Figures 8 and 9 with the shift mechanism setting the torsion bar at a high rate of energy absorption.

Figure 12 is a perspective view of the seatbelt retractor of Figures 8 - 11 showing the coupler in an unactuated condition.

Figure 13 shows the coupler of Figure 12 in an actuated condition.

Figure 14 is an exploded view of the seatbelt retractor.

Figure 15a is a plan view of an improved torsion bar wherein the torsion bar is a single torsion bar diameter with an outer sheath bonded to a portion of the external surface of the torsion bar.

Figure 15b is a plan view of a torsion bar similar to Figure 15a wherein the outer sheath extends covering the entire external surface of the torsion bar.

Figure 16a is a graph showing the energy absorption rates as a function of twist deformation of the torsion bar and torque of a conventional prior art seatbelt retractor having a single diameter torsion bar.

Figure 16b is a graph showing the energy absorption rates as a function of twist deformation of the torsion bar and torque of the improved outer sheath applied on a single diameter torsion bar.

Figure 16c is a graph showing the energy absorption rates as a function of twist deformation of the torsion bar and torque of the seatbelt retractor having a multi load level torsion bar as shown in Figures 1-7 having the transition from high energy load rate to low energy absorption rate in a dashed line with the improved outer sheath bonded to a two piece torsion bar as shown in Figures 8-14 shown in solid lines.

Figure 1 is a perspective cross-section of a seatbelt retractor 10. The seatbelt retractor 10 has a spool 14 upon which is wound a seatbelt 16. The seatbelt retractor 10 allows the belt 16 to protract in the direction of arrow A and to retract in the direction of arrow B. When the seatbelt 16 is protracted in the direction of arrow A, the spool 14 rotates in the direction of arrow Z to wind retraction a spring 17. A retraction spring 17 rewinds the unused portion of the seatbelt 16 in the direction of arrow B by rotating the spool 14 in the direction of arrow Y.

The seatbelt retractor 10 has an inertial sensor 19 that detects changes in vehicle speed. In a crash the inertial sensor 19 actuates a pawl (not shown) that engages and locks the locking wheel 21 in place to limit protraction of the seatbelt 16. To reduce the restraining force of the seatbelt 16 on a vehicle occupant, the seatbelt retractor 10 has a torsion bar 18 that absorbs energy from the spool 14 as the seatbelt 16 protracts. The torsion

bar 18 is mechanically linked to twist and deform with the spool 14. The torsion bar 18 has a first portion 22 and a second portion 26. The first portion 22 has a thicker diameter than the second portion 26. Both portions 22, 26 are deformable. The twisting of the first portion 22 results in the absorption of energy at a relatively higher rate than the twisting of the second portion 26.

The torsion bar 18 acts as a support upon which the spool 14 is rotatably mounted. An end portion 100 of the torsion bar 18 has splines 24 that engage grooves (not shown) in the locking wheel 21 and is rotationally locked in movement with the locking wheel 21. The other end 104 of the torsion bar 18 is rotationally locked in movement with a retraction spring 17. A threaded member 50, a torque tube, is disposed around the torsion bar 18. The threaded member 50 has grooves (not shown) that engage splines 25 of the first portion 22 of the torsion bar 18 so that the threaded member 50 is rotationally locked in movement with the first portion 22.

The torsion bar 18 has splines 33 located near an end portion 104 of the second portion 26. The splines 33 engage grooves (not shown) in a coupler 54 so that the second portion 26 is rotationally locked in movement with the coupler 54. In Figure 7 a threaded member 50 has raised portions 108 that engage holes 112 in the coupler 54. The fit between the holes 112 in the coupler 54 and raised portions 108 of the threaded member 50 is tighter than the fit between the splines 33 of the second portion 26 and the grooves in the coupler 54. When the coupler 54 rotates, it will rotate the first portion 22 of the torsion bar rather than the second portion 26 of the torsion bar, when the coupler 54 is engaged with the threaded member 50 even though the second portion 26 is engaged with the coupler 54.

As shown in Figure 2, during normal operation, the spool 14 is rotationally locked in movement with the torsion bar 18 through the coupler 54, which, at this point, is engaged with the threaded member 50. The threaded member 50 is rotationally locked in movement with a first portion 22 of the torsion bar 18. When the locking wheel 21 is unlocked by the

inertial sensor 19, rotation of the spool 14 causes the torsion bar 18 to wind or unwind the retraction spring 17.

In a crash the torsion bar 18 is selectively actuated to absorb energy from the protraction of the seatbelt 16 at two different rates: a relatively high rate through the first portion 22 and a relative low rate through the second portion 26. Unlike conventional designs, the seatbelt retractor 10 has an additional shift mechanism 30, which selects the rate by which the torsion bar 18 absorbs energy. The seatbelt retractor 10 has two features that control energy absorption providing an additional level of control.

During a crash initially the selection of the rate of energy absorption is made by the control of the positioning of coupler 54 through control unit 58, which determines the appropriate rate by sensing the size and weight of the vehicle occupant through known sensors and programming. After the control unit 58 has made this determination, it controls the position of coupler 54 based on this sensed data.

If a heavy vehicle occupant is sensed, the control unit 58 maintains the seatbelt retractor 10 in the position shown in Figure 2. Here, the coupler 54 is in a position to engage the spool 14 with the first portion 22. When the inertial sensor 19 locks the locking wheel 21 in place during a crash, the end portion 100 of the first portion 22 is prevented from rotating. Withdrawal of the seatbelt 16 in the direction of arrow A transmits a load along a load path 27, i.e., through the spool 14, the coupler 54, the threaded member 50, and the first portion 22. The end portion 100 is locked in place by the locking wheel 21 while, at the splines 25, the first portion 22 will continue to rotate in the direction of arrow Z. The first portion 22 will twist at the splines 25 and absorb energy by deforming. For a heavy vehicle occupant the torsion bar 18 absorbs energy from the spool 14 entirely through the first portion 22 irrespective of the number of crashes. The first portion 22 has sufficient deformability to absorb energy for the anticipated number of crash events.

If the control unit 58 determines that a moderate weight vehicle occupant occupies the seat, it is preferable to slow acceleration of the moderate weight vehicle occupant initially at a high rate than at a slow rate.

Accordingly, the control unit 58 allows the spool 14 to deform the first portion 22 for a predetermined number of turns or a predetermined amount of time and then moves the coupler 54 along an axis X in the direction of arrow C from a first position 62 shown in Figure 2 to a second position 66 shown in Figure 3. As shown in Figure 3 the coupler 54 is decoupled from the threaded member 50 but still remains coupled to the spool 14 at the splines 33 of the second portion 26. The load path 29 is then formed so that a load is transmitted through the spool 14, the coupler 54, and the splines 33 to a second portion 26 of the torsion bar 18. The second portion 26 is locked at the splines 200 to the threaded member 50 and thereby to the first portion 22 of the torsion bar. When the spool 14 rotates in the direction of arrow Z from seatbelt protraction, the spool 14 causes the coupler 54 to twist the second portion 26 of the torsion bar prior to twisting the first portion 22. This has the effect of causing energy from seatbelt protraction to be absorbed at a lower rate by the second portion 26.

For a light weight vehicle occupant, it is preferable to absorb energy from seatbelt protraction at a lower rate at the outset of the crash. The control unit 58 is programmed to shift the coupler 54 from a position 62 to another position 66 immediately so that the load is transmitted along the load path 29 at once as shown in Figure 3. In this manner energy is absorbed by the seatbelt retractor 10 only at the lower rate.

The actuation of the coupler 54 will now be explained with reference to Figures 5 and 6. The control unit 58 is in communication with an actuator 74, a pyrotechnic device which, when actuated, generates a gas in the direction of arrow D. Arrow D is transverse to the axis X. As shown in Figure 6, this gas creates a force 78 on a wall 92 of a member 82. The member 82 then rotates about the axis X in the direction of the arrow Y and rides up on a guide structure 86, such as ramps, causing the member 82 to move in the direction of arrow C. Movement of the member 82 causes movement of the coupler 54 in the direction of arrow C. The member 82 will tend to slide down the guide structure 86 and separate from the coupler 54. This is desirable because otherwise the coupler 54 and the spool 14 will

encounter resistance when the retraction spring 17 rewinds the spool 14. If the actuator 74 is not actuated, the coupler 54 and the member 82 are biased to the bottom of the guide structure 86 by a retaining spring 90.

Control of the energy absorption rate by the control unit 58 is performed by known programming that analyzes the weight and size of the vehicle occupant. The seatbelt retractor 10 has a shift mechanism 30 for shifting between a first portion 22 and a second portion 26. In contrast to the control unit 58, the shift mechanism 30 shifts the seatbelt retractor 10 without reference to the weight or size of the vehicle occupant.

In Figures 1-3, the torsion bar 18 has a threaded member 50 that is linked in rotation with the first portion 22 at the splines 25. When the torsion bar 18 rotates along the direction of arrow Z as the seatbelt 16 protracts the threaded member 50 also rotates. Received on the threaded member 50 is a shift mechanism 30, in this case threaded movable links or runners (see Figure 7). The shift mechanism 30 is linked in rotation with the spool 14 while a threaded member 50 is linked in rotation with the torsion bar 18. Because the torsion bar 18 deforms, the threaded member 50 will rotate at a slower rate than the spool 14, creating relative motion between the spool 14 and the threaded member 50. As shown in Figure 4, this relative motion between the threaded member 50 and the spool 14 causes the shift mechanism 30 to rotate about the threads of the threaded member 50 and thereby to move in the direction of arrow C from a first link position 34 to a second link position 38. When the shift mechanism 30 has reached the second link position 38, the shift mechanism 30 will abut an end portion 39 of the threaded member 50. At this position, the shift mechanism 30 can no longer move in the direction of arrow C. The load from the seatbelt protraction will then be transmitted along a load path 31 through the spool 14, the shift mechanism 30, the threaded member 50 and a first portion 22 of torsion bar 18. The torsion bar 18 will now absorb energy from the spool 14 at a higher rate than the second portion 26.

The shift mechanism 30 shifts automatically and mechanically from a low rate to a high rate of energy absorption. When this shift occurs depends

upon the number of turns the spool 14 is allowed to rotate before the shift mechanism 30 abuts the end portion 39. The number of turns may be based on the anticipated location of the vehicle occupant following airbag deployment. If a second crash occurs the seatbelt retractor 10 is ready to absorb a second impact at a high rate of energy absorption.

For a middle weight vehicle occupant, the control unit 58 allows the first portion 22 to absorb energy from the spool 14 at a high rate, then shifts the coupler 54 from the first coupling position 62 to the second coupling position 66 to allow energy to be absorbed by the second portion 26 at a low rate. Following a predetermined number of turns the shift mechanism 30 shifts back to the high rate of first portion 22. For a light weight vehicle occupant the control unit 58 shifts immediately to a low rate of energy absorption. After a predetermined number of turns the shift mechanism 30 shifts to the high rate of energy absorption. Both the middleweight and the lightweight vehicle occupants are protected in a second crash.

In Figures 8 through 14, an alternative seatbelt retractor 10A is shown. The seatbelt retractor 10A has all the components shown in the retractor 10 illustrated and described with respect to Figures 1 - 7 except that the threaded member 50 is replaced by an outer sheath component 5OA. The outer sheath 5OA as illustrated is die-cast onto the torsion bar 18. The torsion bar 18 is mechanically linked to twist and deform with the spool 14. The torsion bar 18 has a first portion 22 and a second portion 26. The first portion 22 has a larger diameter than the second portion 26 - both portions 22, 26 are deformable. Twisting of the first portion 22 results in the absorption of energy at a relatively higher rate than the twisting of the second portion 26, which absorbs energy at a relatively low rate.

The torsion bar 18 acts as a support upon which the spool 14 is rotatably mounted. One end portion 100 of the torsion bar 18 has splines 25 that engage grooves (not shown) in the locking wheel 21 and is thereby rotationally locked in movement with the locking wheel 21. The other end 104 of the torsion bar 18 is rotationally coupled to a retraction spring 17. In addition, the outer sheath 5OA like the threaded member 50, forms a torque

tube disposed around the torsion bar 18. The outer sheath 5OA as with the threaded member 50 has exterior threads. The sheath 5OA will be formed with grooves (not shown) that by virtue of being cast about the splines 25 of first portion 22 of the torsion bar 18 so that the sheath 5OA is rotationally locked in movement with the first portion 22.

The torsion bar 18 has splines 33 located near an end portion 104 of the second portion 26. These splines 33 engage the grooves (not shown) in the coupler 54 so that the second portion 26 is rotationally locked in movement with the coupler 54. In Figure 14 the sheath 5OA has raised or projecting portions 108 that engage holes 112 in coupler 54. The fit between the holes 112 in the coupler 54 and raised portions 108 of the sheath 5OA is tighter than the fit between the splines 33 of second portion 26 and the grooves in the coupler 54. When the coupler 54 rotates it will rotate the first portion 22, rather than the second portion 26, when the coupler 54 is engaged with the sheath 5OA even though the second portion 26 is engaged with the coupler 54.

In Figure 9 during normal operation the spool 14 is rotationally locked in movement with the torsion bar 18 through the coupler 54, which, at this point, is engaged with the sheath 50A. The sheath 5OA is rotationally locked in movement with the first portion 22 of the torsion bar 18. When the locking wheel 21 is unlocked by the inertial sensor 19 rotation of the spool 14 causes the torsion bar 18 to wind or unwind the retraction spring 17.

In a crash the torsion bar 18 is selectively actuated to absorb energy from the protraction of the seatbelt 16 at two different rates: a relatively high rate through the first portion 22 and a relative low rate through the second portion 26. However, unlike conventional designs, the seatbelt retractor 10A has an additional shift mechanism 30, which selects the rate at which the torsion bar 18 absorbs energy. The seatbelt retractor 10A has two features that control energy absorption thereby providing an additional level of control not found in other seatbelt retractors.

The operation of the seatbelt retractor 10A is the same as previously described with respect to Figures 1-7, with the exception of the threaded

member 50 was mechanically crimped onto the torsion bar 18 whereas the outer sheath 5OA as shown was die-cast onto the torsion bar. The retractor 10A with the outer sheath 5OA shown in Figures 8-14 functions like the retractor 10 with the crimped on mechanically attached threaded member 50 with a improved the performance.

As shown the outer sheath 5OA is a die-cast part formed directly onto the torsion bars 22, 26. The torsion bars 22, 26 are made of steel alloyed and formed to twist multiple times before yielding or breaking. The outer sheath 5OA as shown is made of zinc that at the underlying surface interfaces with the steel torsion bar 22, 26 created a bond capable of resisting a twisting torque up to a point. Beyond this threshold torque the bond quickly and uniformly breaks along its weakest attachment location. For example in the torsion bar 26 of a smaller diameter as the torque is applied and a load is transmitted to the second portion 26 the outer sheath 5OA continues to transfer the torque to the larger diameter portion 22. The load absorption rate will be at the high rate until the bond along the shaft of the portion 26 fails at the interface. The bond of the outer sheath 5OA fails and lets go quickly and uniformly as a function of the circumferential area bonded along the smaller diameter shaft of portion 26 thereafter the retractor drops almost instantaneously to low rate of energy absorption from the pre bond breaking higher rate. This subtle change means the seatbelt payout load transitions from a high load rate to a low load rate more quickly than by the prior mechanical grip method. This is illustrated in Figure 16c.

This feature is applicable to any seatbelt retractor having a torsion bar whether single diameter one piece, a two diameter one piece, or a two diameter two piece component. The outer sheath can be any suitable die- cast material like zinc, 14K gold or a zinc alloy or a molded plastic or composite material wherein the torsion bar is inserted into the outer sheath or the sheath material may be a coated material applied to the surface of a portion of the torsion bar. The breaking of the bond between the surface of the torsion bar and the outer sheath provides an improved rapid transition from a higher energy absorption level to a lower energy absorption level

through the elastic-plastic deformation regions of the loaded torsion members when compared to conventional torsion bars.

A die-cast outer sheath 5OA can be used on a single torsion bar of a uniform diameter as shown in Figures 15a and 15b. In Figure 15a the outer sheath covers a portion of the torsion bar twist shaft whereas in Figure 15b the outer sheath is shown extending across the entire length of the twist shaft of the torsion bar. In a one piece torsion bar having two portions one large diameter shaft portion 22 and a second smaller diameter shaft portion 26 of the outer sheath 5OA can be used.

The outer sheath 50A can be applied on the torsion bars as a coating, molded onto the underlying torsion bars or cast onto the torsion bars. The primary criteria is that a bond is created at the surface interface that can withstand a torque or load higher than at least a portion of the underlying torsion bar as the torsion bar twists it elongates and the diameter narrows such that when the torque twist reaches and therefore starts to exceed the strength of the bond at least a portion of the bond breaks such that the rate of energy absorptions drop quickly making a more rapid transition to the desired rate of energy absorption. For a single diameter shaft torsion bar the outer sheath 5OA breaks the bond across the entire surface interface with the outer sheath 5OA and the underlying torsion bar. The coating, casting, or molded outer sheath 5OA must be sufficiently strong to insure it transfers the loads to break the bond surface are in its entirety on the torsion bar wherein the energy absorption load to be absorbed. This insures the transfer of load rates is virtually instantaneous in a crash.

The die-cast outer sheath 5OA was made of zinc, but could be any zinc alloy or suitable die-cast material. The die-cast outer sheath 50 could alternatively be insert molded into a plastic or composite or resin based polymer outer sheath to achieve a bond sufficient for the purposes. A thick coating could be made of epoxy resin or a similar material to form the outer sheath 5OA.