GB2330338A

GB2330338A - Load limiting device for a seat belt

Info

Publication number: GB2330338A
Application number: GB9721922A
Authority: GB
Inventors: Alan George Smithson; Joseph Patrick Harte; David Blackadder; Andrew Park; John Taylor; Elizabeth Rees
Original assignee: AlliedSignal Ltd
Current assignee: Honeywell UK Ltd
Priority date: 1997-10-14
Filing date: 1997-10-14
Publication date: 1999-04-21
Anticipated expiration: 2017-10-14
Also published as: GB9721922D0; GB2330338B

Abstract

Seat belt webbing for restraining a vehicle occupant, is attached to a structural part of the vehicle via a load limiting device. The load limiting device may comprise a piston-cylinder arrangement having one end fixed with respect to a structural part of the vehicle and the other connected to the webbing so that when the webbing is subjected to a load above a predetermined value, at least a portion of the load is dissipated by the load limiting device, the piston (4) being biased to a retracted position within the cylinder (3) by a spring (5). The load limiting device may alternatively comprise two interleaved relatively rotatable set of discs separated by viscouse fluid. One set of discs is fixed. The other set moves as the seat belt moves. Alternatively a pillar loop bracket can be used with a friction pad connected to the webbing bar to grip the webbing to dissipate load.

Description

SAFETY RESTRRINT 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 autotratically 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 cr 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 occupant's 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 innerTIost 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 propcses improved, simple and more cost effective load limiting arrangetrents 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 piston-cylinder arrangement having one end fixed with respect to a 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, at least a portion of the load is dissipated by the load limiting device, the piston being biased to a position in which it is retracted in the cylinder by a spring to provide the load limiting effect.

According to a preferred embodiment of the first aspect one or preferably two gas generators are provided to selectively and controllably open into the piston side O; the cylinder. One gas generator may be of low capacity and one of high capacity.

A pressure sensor may be arranged in the piston side of the cylinder and used to control the gas generators.

According to a second aspect of the invent ion, 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 two interleaved relatively rotatable sets of discs separated one disk from an adjacent disc by a viscous fluid, one set of discs being fixedly attached to a fixed part of the vehicle and the other set being fixedly attached to a part movable with the seat belt webbing. For example the webbing may be wound on a rotatable bobbin to which the other set of discs is attached.

According to a third aspect of the invent ion, 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 pillar loop bracket having a mounting point for attachment to a fixed part of the vehicle, having at least one bar over which the webbing passes and changes direction, so that the bar is subject to at least a proportion of the load on the webbing, a friction pad connected to the bar and movable in response to loads on the webbing to grip the webbing, the arrangement being such that a load on the webbing causes a corresponding gripping action to be exerted on the webbing thus dissipating a proportion amount of the load.

Preferably two bars or rollers are employed, one on each side of the bracket and advantageously two brake pads, one facing each surface of the webbing, are employed.

According to a fourth aspect of the 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 veSicle via a lcad limiting device, the load limiting device comprising a relatively low level load limiter fixed at one end to a structural part of the vehicle, and connected at its other end to a cable, a drum fixed relative to the structural part of the vehicle, about which drum the cable is wound, on attachment point fixed to the other end of the cable which attachment point is attached in the force path of the webbing so as to be subjected to loads exerted on the webbing. Preferably the cable is wound at least three times around the drum.

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 load limiting arrangement according to the first aspect of the invention; Figure 2 is a cross-sectional vie of the apparatus of Figure 1; Figure 3 is a graph showing load against time for the apparatus of Figures 1 and 3; Figure 4 is a part cut-away view of a load limiter according to a second aspect of the Invention; Figure 5 is a cross-sectional view of the load limiter of Figure 4; Figure 6 is a side perspective vieW of a load limiter according to a third aspect of the invention; Figure 7 is a cross-sectional side view of the arrangement of Figure 6; Figure 8 is a graph showing load against extension for the apparatus of Figures 6 and 7; Figure 9 illustrates a load limiting arrangement which can be used with the arrangements of Figures 1 to 8 or with any other load limiting arrangement.

Shown in Figures 1 to 3 is a pyrotechnically controlled load limiter. One end is anchored to a fixed part of the vehicle via anchor point 1, and the other end is attached to seat belt webbing, or to the buckle, or to a retractor, via slot 2. Between these two fixing points is a pressure tub 3 in which is located a piston 4 biased by a spring 5 to stop the piston creeping forward during normal use. Gas generators 6, 7 are arranged to supply gas under pressure to the piston side of the pressure tube 3. Preferably the gas generators 6, 7 are of different capacities, for example one may be a high pressure gas generator and one a low pressure gas generator. The gas generators may be actuated in a variety of firing options: only one operated, both simultaneously, or both fired at different times depending on the load limiting required by the prevailing conditions.

A pressure sensor 8 is arranged in the side of the pressure tube 3, on the piston side and data from this pressure sensor 8 may be used as feedback data to a control unit (not shown).

Space 9 is provided in the cylinder 3, on the other side of piston 4 and this additional space allows the device to act as a pretensioner, i.e. one or more of the ga generators firing drives gas into the space behind thf piston 4 and pushes it into cylinder space 9, thus pullinc in the attachment point 2 and thus drawing in a length of webbing.

The graph in Figure 3 illustrates one possible loac limiting effect over time using the load limiter of Figure 1 and 2. Initially the load rises as the crash pulse builds. At time TO the load reaches a level Ls high enough to overcome the bias and inertia of the spring 5 and the piston 4 is pulled (to the right in the Figures) allowinc limited webbing payout and absorbing some of the load ac indicated by the flattening of the graph At time Tl one of the gas generators (6, 7) in this example, the low pressure gas generator, fires, and the load limiting effect of thw gas behInd the piston 4 combines with that of the spring to raise the level of load limiting to Lgl. A little late at time T2 the second, high pressure gas generator, fires, raising the level of load limiting to Lg2. Of course, where required only a single gas generator may be fired or bot) may be fired at the same time. Also the high pressure gac generator may be fired at a time before the low pressure gac generator. The exact sequence of timing will depend upor the conditions of load limiting requ wed by the rest of thE safety belt system and may also be tailored to the conditions existing in the vehicle at the time of the emergency, for example to the weight of the seat occupant to the severity of the crash, to whether an airbag ie installed/deployed or to any other factors.

In Figures 4 and 5 a load limiting arrangement employing viscous coupling is illustrated. Seat belt webbing 10 is wound on a spool 11 mounted for rotation about a shaft 12 supported in a frame 13 which is attached to a fixed part of the vehicle by mounting hole 17. The spool 11 may be the spool of a retractor or may be another bobbin arranged elsewhere in the seat belt system. The load limiting arrangement comprises rotating disc blades 14 attached to the spindle 12 of the spool 11 interleaving with fixed vanes 15 attached to the housing 13. The space 15 between the disc blades 14 and the vanes 15 is filled with viscous fluid.

At low levels of load felt by the webbing 10 in the payout direction A, the viscosity of the fluid does not provide sufficient friction to keep the rotatable disc blades 14 effectively bound to the fixed vanes 15 and thus allows the spool 11 to rotate freely. However at loads over a predetermined level, for example the loads felt at the peak of a crash pulse, the viscosity of the fluid acts as a break allowing only a very slow rotation of the sets of blades 14 relating to the vanes 15 allowing very slow extraction of the webbing in the direction A and thus absorbing some of the peak loads which would otherwise b felt by the vehicle occupant.

Figures 6 and 7 show a load limiting arrangement incorporated into a pillar loop, otherwise known as a Dring. This is the shoulder level bracket, fixed to the side pillar of the vehicle, to support the seat belt webbing as it changes direction from the vertical line as it extends from the retractor on the floor of the vehicle, to a diagonal line across the torso of the vehicle occupant.

The pillar look bracket or D-ring 20 has fixing hole 21 through which it is attached to the vehicle side (B) pillar.

It comprises brake pads 22 and 23 arranged above and below a slit 24 through which the webbing 10 passes. On either side of the slit 24 are rollers 25 and 26 attached to the upper brake pad 22. A downward force on these guide rollers 25 and 26 will apply pressure to the upper brake pad 22 and trap the webbing between the brake pads 22 and 23. The higher the downward force on the rollers, the larger the clamping force on the webbing. Thus the higher the load on the webbing 10, the higher the load limiting effect is.

This is shown clearly by the graph in Figure 8. Effectively then the pillar loop amplifies the load.

The amplification factor is given by: F2 = F1 ( 1 + 2 ) 2 Cos # Where: F = effective load on the diagonal part of the webbing Fl = the load on the vertical part of the webbing e = angle made to the vertical by the diagonal part of the webbing Ii = co-efficient of friction of brake pads 22 and 23 This arises since the forces exerted on the upper brake pad is given by the sum of the force on the vertical part of the webbing Fl and the vertical component of the force on the diagonal part of the webbing (F2 Cos e). The force on the diagonal part of the webbing F2 is the sum of the force on the vertical part of the webbing F; and the friction force caused by the brake pads which is given by the force on the upper brake pad times the co-efficient of friction of each of the upper and the lower brake pads (2 ) Figure 9 shows a load limiting arrangement using the well known capstan effect. This is effectively an amplification system and could be used in conjunction with any other load limiting arrangement. It allows a relatively cheap, low level limiter to be used but amplifies the effect it produces. Thus a low level load limiter 30 is connected to a fixed part of the vehicle at its end 31. This low level load limit may be a form of piston cylinder arrangement or a spring. At the other end of the load limited a cable 32 emerges and is wound around a fixed drum 33 for many turns. The end of the cable 32 is attached to a bracket 34 to which seat belt webbing is attached Alternatively the bracket 34 may be attached to a buckle mounting point or to a retractor mounting point. The fixed drum 33 is mounted on fixing plate 35 which is attached to a fixed part of the vehicle A load on the webbing, as in a crash, causes a force to be exerted on the bracket 34 in the direction of arrow F3.

This pulls on the cable 32 in a direction to unwind it from the drum 33. The effect of the friction between the cable turns and the drum 33 absorbs some of the load of Fm3s before the load is felt by the low level load limiter 30. Thus the relatively low level load limiter 30 can effectively absorb much higher loads than would otherwise be the case. The load effectively felt by the low level load limiter is Fiow.

The amplification effect of this capstan arrangement can be calculated from: Frnax = E uO x F Where: H = coefficient of friction e = the angle at which the wire is wrapped around the fixed drum (in radians) Hence for three revolutions with a co-efficient of friction (U) equals 0.2 an amplification factor of about 43 is given. Hence a 6 K-Newtons load can be absorbed by a low level load limiter capable of absorbing only 130 Newtons.

Claims

CLAIMS: 1. 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 piston-cylinder arrangement having one end fixed with respect to a 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, at least a portion of the load is dissipated by the load limiting device, the piston being biased to a position in which it is retracted in the cylInder by a spring to provide the load limiting effect.
2. A vehicle safety restraint according to claim i wherein a gas generator is provided and is arranged to selectively and controllably open into the piston side of the cylinder.
3. A vehicle safety restraint according to claim 2 wherein two gas generators are provided and arranged to selectively and controllably open into the piston side of the cylinder.
4. A vehicle safety restraint according to claim 3 wherein one gas generator is of low capacity and one is of high capacity.
5. A vehicle safety restraint according to any one of claims 2 to 4 further comprising a pressure sensor arranged in the piston side of the cylinder and arranged to control the or each gas generator.
6. 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 two ,nterleaved relatively rotatable sets of discs separated one disk from an adjacent disc by a viscous fluid, one set of discs being fixedly attached to a fixed part of the vehicle and the other set being fixedly attached to a part movable with the seat belt webbing.
7. A vehicle safety restraint according to claim 6 wherein the webbing is wound on a rotatable bobbin to which the other set of discs is attached.
8. 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 pillar loop bracket having a mounting point for attachment to a fixed part of the vehicle, having at least one bar over which the webbing passes and changes direction, so that the bar is subject to at least a proportion of the load on the webbing, a friction pad connected to the bar and movable In response to loads on the webbing to grip the webbing, the arrangement being such that a Icad on the webbing causes a corresponding gripping action to be exerted on the webbing ths dissipating a proportional amount of the load.
9. A vehicle safety restraint according to claim 8 further comprising two bars employed, one on each side of the bracket, ar.d two brake pads, arranged one facing each surface of the webbing.
10. 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 relatively low level load limiter fixed at one end to a structural part of the vehicle, and connected at its other end to a cable, a drum fixed relative to the structural part of the vehicle, about which drum the cable is wound, on attachment point fixed to the other end of the cable which attachment point is attached in the force path of the webbing so as to be subjected to loads exerted on the webbing.
11. A vehicle safety restraint according to claim 10 where in the cable is wound at least three times around the drum.
12. A vehicle safety restraint substantially as hereinbefore described with reference to figures 1 to 3 or figures 4 and 5 or figures 6 to 8 or figure 9 of the accompanying drawings.