GB2330337A - A load limiting arrangement for a seat belt - Google Patents

Abstract

Seat belt webbing is attached to a structural part of the vehicle via a load limiting device, the load limiting device comprising a torsion bar having one end fixed with respect to the structural part of the vehicle and the other end connected to the webbing so that when the webbing is subjected to a load above a predetermined value, the torsion bar twists and absorbs energy. The torsion bar may be connected via a lever arm link or may be mounted in a knurled or toothed roller or connected to a pinion wheel arranged to deform a rack. The load limiting arrangement can be mounted beneath a vehicle seat.

Description

SAFETY RESTRAINT DESCRIPTION The present invention relates to a safety restraint for use in a vehicle and particularly to a seat belt.

Modern seat belts comprise a length of webbing arranged to pass diagonally across the torso of a vehicle occupant and generally horizontally across the hip region of the vehicle occupant (so-called lap portion of the belt). This is known as a three point belt system. One end of the belt webbing is firmly attached to a structural part of the vehicle such as the floor, and the other end is attached to the spool of a retractor which itself is firmly attached to a structural part of the vehicle, usually the side Bpillar. Between the retractor and the fixed point, a fastening element such as a metal tongue is fixed to the belt with which it can be fastened into a buckle which itself is attached to fixed part of the vehicle on the other side of the occupant seat to the retractor.

The retractor has a clock spring which automatically keeps any slack in the belt wound onto the spool and thus keeps a tension in the belt. The clock spring allows pay out of webbing under the influence of relatively gentle forwardly directed inertia of the vehicle occupant, for example to allow for normal movement of the occupant such as occurs when he reaches forward to activate in car controls, or access glove compartments or door pockets.

In the event of a crash the sudden high forward momentum of the occupant activates a crash sensor which locks the spool against rotation and restricts forward motion of the occupant to prevent him colliding with the internal fixtures of the vehicle such as the steering wheel, dashboard or windscreen.

However it has been found, particularly in high velocity crashes, that the sudden locking of the seat belt can itself cause injury to the occupant due to the sudden impact of the torso with the belt webbing.

In recent years it has been proposed to introduce a load limiting effect into the seat belt system so as to allow a limited and controlled forward motion of the occupant after the retractor has locked. This decreases the forces exerted by the belt on the occupants torso.

Load limiting proposals are described in EP 0 297 537 wherein a plastically deformable member is used in the retractor, and particularly between the spool and innermost winding of the belt webbing. Alternative load limiting proposals are known in which crushable bushings or nuts or deformable torsion bars are placed within the retractor in the force path between the spool locking mechanism and belt webbing. These proposals are complex and expensive and require the retractor to be specially designed and constructed to incorporate them.

The present invention proposes improved, simpler and more cost effective load limiting arrangements for seat belts.

According to one aspect of the present invention there is provided a vehicle safety restraint comprising seat belt webbing for restraining a vehicle occupant, the webbing being attached to a structural part of the vehicle via a load limiting device, the load limiting device comprising a torsion bar having one end fixed with respect to the structural part of the vehicle and the other end connected to the webbing in the path of forces exerted on the webbing so that, when the webbing is subjected to a load above a predetermined value, the load is transferred to said other end of the torsion bar as a turning motion thereby to twist the torsion bar, and absorb energy.

According to one embodiment of the invention the torsion bar is offset from the force path and has one end connected by a lever linkage to the belt webbing and the other end connected to the structural part of the vehicle.

The torsion bar may be mounted in a knurled or toothed roller arranged in a roller housing for translational movement and to engage the webbing when the load on the webbing is above a predetermined value.

Such an arrangement may be mounted under a vehicle seat for optimum unobtrusiveness.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made to the accompanying drawings, in which: Figure 1 is a perspective view of a first embodiment of the invention.

Figure 2 is a perspective view of a variation of the embodiment of Figure 1.

Figures 3 to 5 are diagrams illustrating how the embodiment of Figure 2 operates under load.

Figures 6 is a perspective exploded view of another embodiment of the invention.

Figure 7 illustrates the embodiment of Figure 6 in sectioned assembled view from a different angle.

Figure 8 is a perspective view of a further embodiment of the invention.

In the embodiment of Figure 1 a torsion bar 1 has one end connected to seat belt webbing 2 via a bearing bracket 3 and a lever arm 4 welded to the torsion bar 1 at 5. The other end of torsion bar 1 is welded to a second bracket 6 attached to a fixed part of the vehicle.

As the load increases on the webbing 2, for example during the crash pulse of an accident, a turning force F is generated on the lever 4 which transfers torque to one end of the torsion bar 1. Resistance of the torsion bar 1 to twisting determines the load limiting effect of the torsion bar and this can be adapted to provide specific load limiting conditions by appropriate choice of the length, diameter and material of the torsion bar 1. This form of torsion bar is easily fitted under the seat in a vehicle and is thus unobtrusive and does not occupy an undue amount of space in the vehicle.

In Figure 2, a form of torsion bar is illustrated at la. This is formed by one of the arms of in a bent wire loop 10. Webbing 2 is folded and stitched along lines 12 to form a loop 11 around the torsion bar loop arm la. The wire loop 10 is attached to a fixed anchorage point of the vehicle by a rivet or screw through ring 13 at the other end of the loop 10.

Figures 3 to 5 illustrate the operation of this form of torsion bar. Figure 3 illustrates the unloaded condition in which the webbing 2 is wound around the two generally horizontal atoms of the wire loop 10. In Figure 4 a load is applied to the webbing in the direction F. This pulls on the lower arm 14 of wire loop 10 and causes a twisting motion in the top arm la (i.e. the torsion bar) of loop 10.

Thus, at a predetermined load, a set amount of webbing extension is allowed.

In Figure 5 the force F has increased and the wire loop 10 has twisted further into an almost fully extended position allowing maximum pay out of the belt webbing.

In Figures 6 and 7 torsion bars 1 are set in knurled or toothed rollers 15 mounted in a fixed housing 16. The housing 16 is fixed relative to the vehicle and the webbing 2 passes between the rollers 15 as illustrated in Figures 6 and 7. The torsion bars 1 are held in the ends of housing 16 by hexagonal cut-out holes 17 Figure 8 illustrates another embodiment of the invention in which the torsion bar 1 is supported in a mounting frame 18 with one end 19 fixed in the mounting frame 18 and the other end passing through a hole 20 in the mounting frame and connected to a pinion wheel 21. The pinion wheel 21 is arranged to engage with appropriately dimensioned teeth on a rack 22. The rack 22 is attached via slot 23 to a buckle anchorage or another part of the safety belt webbing. When the safety belt is under load the rack moves in the direction of arrow M turning the pinion wheel 21 and twisting the torsion bar 1, thus absorbing some of the load of the crash.

Claims (8)

1. CLAIMS i. A vehicle safety restraint comprising seat belt webbing for restraining a vehicle occupant, the webbing being attached to a structural part of the vehicle via a load limiting device, the load limiting device comprising a torsion bar having one end fixed with respect to the structural part of the vehicle and the other end connected to the webbing in the path of forces exerted on the webbing so that, when the webbing is subjected to a load above a predetermined value, the load is transferred to the other end of the torsion bar as a turning motion thereby to twist the torsion bar and absorb energy.
2. 2. A vehicle safety restraint according to claim 1, wherein the torsion bar has one end connected by a lever lInkage to the belt webbing and te other end connected to the structural part of the vehicle at a position offset from the force pa=h.
3. 3. A vehicle safety restraint according to claim 1 wherein the torsion bar comprises one arm of a bent wire loop.
4. 4. A vehicle safety restraint according to claim 1, wherein the torsion bar is a knurled or toothed roller which is mounted in a roller housing and arranged for translational movement into engagement with the webbing, when the load on the webbing is above a predetermined value.
5. 5. A vehicle safety restraint according to claim 4 wherein the torsion bar is held in the housing by a hexagonal hole.
6. 6. A vehicle safety restraint according to claim 1 wherein the torsion bar is supported in a mounting frame with one end fixed in the mounting frame and the other end connected to a pinion wheel, which is arranged to engage with a rack attached to a fixed anchorage of the vehicle.
7. 7. A vehicle safety restraint according to any one of the preceding claims adapted for mounting under a vehicle seat.
8. 8. A vehicle safety restraint substantially as hereinbefore described with reference to Figures 1 to 5 or Figures 6 and 7, or Figure 8 of the accompanying drawings.