GB2327919A

GB2327919A - Force limiting device for seat belt

Info

Publication number: GB2327919A
Application number: GB9801850A
Authority: GB
Inventors: Alan George Smithson
Original assignee: AlliedSignal Ltd
Current assignee: Honeywell UK Ltd
Priority date: 1997-07-28
Filing date: 1998-01-28
Publication date: 1999-02-10
Anticipated expiration: 2018-01-28
Also published as: GB2327919B; GB9715937D0; GB9801850D0

Abstract

A force limiting device limits the force on a seat belt wearer due to activation of a seat belt pretensioner and is provided with means to selectively set the level of force limitation. The device is connected between a seat belt and an anchor point and may comprise an outer tube 20 containing a series of deformable inner tubes 121 (a, b and c) and a first disc 131 attached to a pull rod 130. In the event of a crash, movement of the seat belt wearer and activation of a seat belt pretensioner pulls the pull rod 130 and the outer tube 20 in opposite directions. Below a predetermined level of force any movement of the pull rod 130 is prevented by the contact between a first disc 131 and the inner tubes 121. Above the predetermined level of force the inner tubes 121 deform thereby limiting the maximum force applied to the seat belt wearer. The level of force limitation can be increased by rotating the pull rod 130, either manually or electrically, so that tab 132 engages a second disc 134 of a greater diameter than the first disc 131 thus increasing the force on the pull rod 130 required to deform the inner tubes 121.

Description

PRETENSIONER DESCRIPTION The present invention relates to a pretensioner for a vehicle safety restraint and particularly to a load limiting arrangement there for.

A typical restraint system as used in passenger cars comprises a lap and a diagonal webbing restraint in which the webbing pays out from a webbing retractor and, via a shoulder-height guide loop, passes diagonally downwards to a buckling tongue engageable in a buckle anchored on one side of the passenger seat. The webbing then passes across the seat (as a lap restraint) to a final anchorage point at the other side of the seat. With such a system, localised and very substantial forces are exerted on the occupants body in restraining the occupant in the event of a crash.

Moreover, the forces exerted on the diagonal part by the occupant can be such as to result in tightening the lap part of the webbing around the hips of the occupant accompanied by some pay-out of the diagonal portion. Such pay-out therefore allows forward movement of the head and shoulders.

This can itself result in injury due to impacts with parts of the interior of the vehicle and forces exerted between the webbing and an occupant can also cause injury.

The object of the present invention is to reduce and control forces exerted between a seat belt restraint and an occupant and thereby reduce the possibility of injury resulting from a crash situation.

Such a system is known from applicant's own EP 0 568 327 A.

According to the present invention there is provided a pretensioner for a vehicle safety restraint system, the system comprising a first and a second, higher level, force limiting means located between the safety restraint and an anchorage point for the safety restraint, there being means for switching between the first and the second force limiting means.

Preferably the pretensioner comprises a piston-cylinder arrangement, and the force limiting means comprises a frangible or deformable supporting tubular member and first and second deforming members and the switching means comprises means for applying the pretensioning force through either the first or the second deforming member wherein the second deforming member is of larger diameter than the first so as to apply a higher level of force limitation.

According to a preferred embodiment of the present invention the deformable supporting tubular member comprises a plurality of segments, each of which has a different deformable internal profile, for example, different numbers and/or different sizes of internal radially extending ribs, or different materials. The deforming member comprises discs of respective different radii, for example to deform or shear respective different numbers of ribs, or ribs in different segments of the supporting tubular member, so as to contribute different force limitation levels.

One disc of relatively small diameter, providing low level force limiting, may be permanently attached to a connecting rod.

The second disc, of larger diameter, to provide higher level force limiting, may be selectively connectable to the rod, as for example by provision of a slot in the second disc and a tab on the connecting rod which in one orientation passes through the slot in the second disc and in another orientation, eg at a 900 angle, engages the disc so as to activate it in force limiting manner. Hence, rotating the connecting rod through 90" selectively engages or disengages the second disc, and thus switches between low level and high level force limitation.

More discs of different diameters may be provided to provide more levels of force limiting, and can be arranged to be selectively connectable in the force transfer path to allow switching between the different levels.

The discs are preferably provided with shear pins to determine a minimum force at which each becomes operative in the force limiting path.

The internal profile of the control segments of the deformable supporting member and the diameters of the discs are chosen to suit the load/extension characteristics required by the system. High levels of force limitation are given for example by discs of higher diameter causing higher interference with the internal profile of the segments, by a large number of ribs and by use of a harder material or one with a greater coefficient of friction either for the discs or for the control segment ribs.

In general these factors are determined before the assembly is completed and installed in the vehicle. However according to one embodiment, an expanding disc is provided.

The disc is expanded by a nut driving it up a cone with a low friction coating. This allows for a continuous stepless variation in the load level.

The nut preferably has a multi-start thread and is driven by a control arm engaging in a cam track. The cam track may for example, be mounted stationary relative to the vehicle chassis, while the load limiter is attached to a vehicle seat. The level of load limiting can then be controlled as a function of seat position with the arrangement such that when the seat is in the forward most position (indicative of a small, light occupant) the load limiting is at its lowest level, eg the smallest diameter of the disc. As the seat moves back indicating a larger, heavier occupant, the control arm moves along the cam track, rotating the nut and driving the disc up the surface of the cone to expand the disc and increase the load level. Thus the shape of the cam track can be adapted to determine a suitable load level for any given seat position.

Alternatively the nut and disc can be driven by rotating cables or gearing connected to be sensitive to the seat position, or by electrical means - for example electronic sensors in the seat could measure the weight of the occupant and adjust the load level accordingly, or sensors could detect the angle of rearview or wing mirrors as an indication of the occupants size and position, and adjust the load level accordingly. As a further alternative, or in addition, the vehicle velocity and/or the severity and angle of crash can be taken into account and the load level adjusted. A microprocessor can be programmed with appropriate adjustment values to take into account of the factors involved.

The expanding disc is constructed to act as a diaphragm spring so as to tend to its smallest diameter, and contract naturally as it moves down the cone when the nut moves away, eg as the seat is adjusted forward for a small occupant. In any case, if the disc jams at a large diameter this is the fair/safe higher load level and once load limiting starts, the disc will be forced down the cone.

It will be understood that many different force limitation systems could be applied to the present invention.

For a better understanding and to show how the same may be carried into effect, reference will now be made to the accompanying drawings in which: Figure 1 illustrates a typical vehicle occupant safety belt arrangement with a pretensioner.

Figure 2 is a cross-sectional view of a load limiter tube according to one embodiment of the present invention for use in the arrangement of Figure 1.

Figures 31 32 and 3, show alternative cross-sectional profiles for control segments for the load limiter tube of Figure 2.

Figure 4 illustrates in exploded view the load limiter of figure 2.

Figure 5 is an exploded view of a second embodiment of the invention.

Figure 6 is a cross-sectional view of the embodiment of figure 5.

Referring to Figure 1, the vehicle passenger restraint system includes a seat having a seat squab portion 1 and a seat back portion 2, the latter typically being manually tiltable in a conventional manner. In this particular example the seat is installed as a front seat in a passenger car and the restraint webbing is fed out from an emergency locking type of webbing retractor 9, at the bottom of the "B" post of the car body at one side of the seat. The webbing passes through a shoulder height guide loop at 3 and then diagonally downwards as at 4 across the torso of an occupant to a buckling tongue 5 engaged in a buckle anchored on the other side of the seat. Webbing 6 coming away from the buckling tongue passes across the lap of the occupant to a connection to an anchoring means 7 on the side nearest the viewer of the drawing. The anchoring means 7 incorporates a force limiting device 8 designed and constructed to submit in a controlled manner to a predetermined limited force value by way of movement whilst sustaining forces up to said value.

Considering now the operation of the system, in the event of a frontal collision being encountered by the vehicle the emergency locking retractor senses a predetermined deceleration value of the vehicle and the retractor locks the torso webbing portion 4 against withdrawal movement via the retractor 9. As the collision progresses the deceleration increases as do the inertial forces exerted by the occupant on the belt portion 4 and the belt portion 6 of the restraint. When the tension in the portion 6 attains a predetermined force limit value (typically 5 KN) the force limiting device 8 submits to such initial maximum force to the extent of permitting pay-out whilst maintaining no more than such as a restraining force at the anchorage 7. Such pay-out allows a few centimetres of forward movement of the portion 8 and occupant at the hips and since some sliding of the belt can occur at the buckle, forward movement has the effect of transferring kinetic energy of the occupant progressively as power to the force limiting device and thereby limiting the level of the impulsive forces applied to the occupant by the safety restraint webbing and also thereby reducing the probability of head and neck injury occurring.

In Figure 1, diagrammatic illustration is given of the extent of torso movement (A) of a seat occupant with a force limiting device fitted to the restraint system and the extent of torso movement (B) of an occupant restrained by a system without such a restraint fitted. In (A) the hips of an occupant are permitted to move in a controlled manner due to the limiter introducing slack to the lap portion of the belt. The upper torso then tends to move in a translational manner rather than pivoting excessively about the hips.

Forward movement of the occupants head and chest is thereby less as also are the sustained belt forces.

A preferred form of force-limiting device is illustrated in Figure 2 which shows an outer metal tube 20 which forms a main housing. Conveniently the metal tube 20 is of steel and is mounted horizontally in the vehicle body and adjacent the door sill of the vehicle and a cable 22 is led into an approximately vertical direction (not shown) as it passes through anchoring device 7.

Within the outer tube 20 is an inner deformable or frangible tube 121 formed in three sections 121a, 121b, 121c with internal profiles as shown in Figures 31t $ and k respectively. This shows upper and lower levels of load in relation to webbing extension. The inner tube 121 is preferably formed of metal such as aluminium or mild steel and may be extruded.

The control segments have internal profiles as illustrated with different numbers of internal radially extending ribs to present different force limiting characteristics, obviously the more ribs the higher value force limiter. These are shown more clearly in Figure 2.

The control segments 121a, 121b and 121c,fit into the outer tube 20.

Figure 4 shows the switching system for changing between different levels of force limitation. A pull rod 130 is connected to a low level, small diameter, disc 131 and has a control tab 133 in a second control disc 134. The second control disc 134 is of slightly larger diameter than the first, and has shear pins 135 which are connected to the inside of the end cap 136 to determine a minimum level at which the second, higher level, disc 134 becomes operative in the force limitation path.

If the second disc 134 is to be brought into play then the control rod is twisted through 900 so that the control tab 132 engages the side of the disc 134 facing away from the first disc. The pull rod 130 may be rotated by an electrical signal from a sensor or manually if desired.

Of course further discs of various diameter may be incorporated to provide more levels of force limiting.

Figures 5 and 6 illustrate another embodiment in which the load level is adjustable. Like parts are indicated by like reference numerals. Thus the load-limiter comprises an outer steel tube 20 within which are located three inner deformable or frangible tubes 121a, 121b and 121c, each formed with different internal profiles (eg different numbers of internal ribs as shown) A pull rod 130 has a cone 140 at one end and a threaded section 141 to receive a nut 142. An expandable disc 143 rides on the cone 140. Connected to nut 142 is a control member 144 with a control arm 145 jutting radially outward to engage cam track 146 in cam plate 148. End cap 147 closes the tube 20 to complete the assembly.

In operation the cam plate is held stationary, for example being mounted to the chassis of a vehicle, while the load limiter is attached to a vehicle seat. As the seat is adjusted the control arm 145 moves in cam track 146, rotating and turning the nut 142 on the rod threading 141.

This pushes the expandable disc 143 up the cone 140 and gives the disc a larger diameter which increases the interference with the frangible tubes and hence increases the load level.

Thus a larger heavier occupant who has the seat adjusted to a more rearward position will experience a higher load level than a small light occupant who adjusts the seat forwardly. This gives much more satisfactory restraining performance in a crash situation, adapted accurately to the occupants specific requirements.

Claims

1. A pretensioner for a vehicle safety restraint system, the pretensioner comprising force limiting means located between the safety restraint and an anchorage point for the safety restraint, the force limiting means being selectively operable at a first and at a second higher level of force limiting, and there being means for switching between the first and the second force limiting means.

2. A pretensioner according to claim 1 wherein the pretensioner comprises a piston-cylinder arrangement, and the force limiting means comprises a frangible or deformable supporting tubular member and first and second deforming members, and the switching means comprises means for selectively applying the pretensioning force through one of the first or the second deforming members, wherein the second deforming member is of larger diameter than the first member so as to apply a higher level of force limitation.

3. A pretensioner according to claim 2 wherein the supporting tubular member comprises a plurality of segments, each one having an internal deformable profile different to that of the other segments, wherein each different profile has a different number of internal radially extending ribs.

4. A pretensioner according to claim 2 wherein the supporting tubular member comprises a plurality of segments, each one having an internal deformable profile different to the profile of the other segments, wherein each different profile has a different size of internal radially extending ribs.

5. A pretensioner according to claim 2 wherein the supporting tubular member comprises a plurality of segments, each one having an internal deformable profile different to the profile of the other segments, wherein each different profile is formed of a different material.

6. A pretensioner according to any one of claims 3 to 5 wherein the deforming member comprises a plurality of discs each one having a different radius to the other discs and being arranged, to deform or shear respective different numbers of ribs internal in the tubular member.

7. A pretensioner according to any one of claims 1 to 5 wherein the deforming member comprises a plurality of discs each one having a different radius to the other discs and being arranged to deform or shear ribs in different segments of the supporting tubular member, so as to contribute different force limitation levels.

8. A pretensioner according to any one of the preceding claims wherein the deforming member comprises a first disc of relatively small diameter, providing low level force limiting, permanently attached to a connecting rod and a second disc, of larger diameter to provide higher level force limiting, selectively connectable to the rod.

9. A pretensioner according to claim 8 wherein a slot is provided in the second disc and a tab is provided on the connecting rod which, in one orientation, passes through the slot in the second disc, and, in another orientation, engages the disc so as to activate it in force limiting manner, so that rotating the connecting rod switches between low level and high level force limitation.

10. A pretensioner according to any one of claims 6 to 9 wherein at least one of the discs is provided with at least one shear pin to determine a minimum force at which the or each disc becomes operative in the force limiting path.

11. A pretensioner according to claim 1 or 2 wherein the force limiting means comprises an expandable disc mounted on a cone and expandable from a small diameter to a larger diameter by a nut driving the disc up the cone.

12. A pretensioner according to claim 11 wherein the cone is coated with a low friction coating.

13. A pretensioner according to claim 11 or 12 wherein the nut has a multi-start thread and is driven by a control arm engaging in a cam track.

14. A pretensioner according to claim 11, 12 or 13 wherein the cam track is mounted stationary relative to the vehicle chassis, with the load limiter attached to a vehicle seat so that the level of load limiting can be controlled as a function of seat position.

15. A pretensioner according to claim 11, 12 or 13 wherein the nut and the disc are driven by electrical means sensitive to the seat position.