GB2332397A

GB2332397A - Load limiting device for seat belt pretensioner

Info

Publication number: GB2332397A
Application number: GB9726855A
Authority: GB
Inventors: Alan George Smithson
Original assignee: Breed Automotive Technology Inc
Current assignee: Breed Automotive Technology Inc
Priority date: 1997-12-18
Filing date: 1997-12-18
Publication date: 1999-06-23
Anticipated expiration: 2017-12-18
Also published as: GB2332397A9; GB2332397B; GB9726855D0

Abstract

Load limiting device for a gas operated seat belt pretensioner comprising a vent 23 for venting pretensioning gas, a seal 24 for sealing the vent 23 and means to rupture the seal 24 after activation of the pretensioner. The rupture means may take the form of sharpened teeth 21 arranged on a flange 20 of the seat belt spool 22, the teeth being angled so that rupture of the seal 24 occurs only on pay-out of the seat belt. Alternatively the rupture means may be attached to, and movable with, the seat belt webbing in such a way so as to break the seal only on pay-out of the seat belt. The seal 24 is preferably bulbous with a U-shaped cross-section and resilient so that it remains in a retracted position (as shown in figure 2) until extended by the release of pretensioning gas (to the position shown in figure 3). In the event of a crash, after pretensioning has occurred rupture of the seal 24 and subsequent venting of pretensioning gas allows a small amount of seat belt pay-out thereby limiting the maximum force applied by the seal belt to the seat belt wearer.

Description

1 RETRACTOR 2332397 The present invention relates to a retractor for a

vehicle safety restraint seat belt and particularly to a 5 retractor fitted with a gas operated pretensioner.

Pretensioners are used in modern restraint systems to rapidly draw in a length of belt Webbing in the event of a crash to take up slack in the belt and thus to minimise the forward movement of the restrained person and to more correctly position the person in the vehicle seat to maximise the effect of a secondary safety restraint such as an airbag.

The pretensioner may be arranged to pull back the belt at the buckle mounting or to rewind belt webbing onto the retractor.

In high velocity crashes, the force exerted on the vehicle occupant by the restraining seat belt itself, is very high and can itself cause injury. Modern systems therefore incorporate load limiting features to reduce this effect. The ideal system tightens the seat belt at the very beginning of a crash, as the crash force is rising but then allows a small amount of payout at a controlled load, at the peak of the crash force, to reduce the load felt by the vehicle occupant.

Many different load limiting arrangements have been proposed including torsion bars connected to the retractor spool, and arrangements in which substances are compressed 2 or are extruded through narrow orifices.

The present invention aims to provide an improved retractor with loadlimiting features.

According to one aspect of the present invention there is provided a retractor comprising: a rotatable spool fixedly connected to a toothed ratchet wheel, a locking pawl for engaging with the ratchet wheel to lock the spool against rotation in the event of a crash, a vent hole for venting gas from a pretensioner, a seal for the vent hole, wherein the teeth on the ratchet wheel are asymetric and are angled so that, in the pretensioning direction of rotation of the ratchet wheel, the teeth present sloping ramp surfaces to the seal, whereas, in the direction of rotation opposite to the pretensioning direction, the teeth present a generally sharp edge substantially toward the seal to rupture it.

According to a second aspect of the invention there is provided an arrangement for venting a pretensioner for a vehicle safety restraint, the arrangement comprising a venting duct connected to a source of pretensioning gas, the duct having a vent hole and a seal f or the vent hole, the seal being responsive in its positioning to the gas pressure, there being means, movable with the seat belt webbing which breaks the seal when the webbing moves in one direction and which does not break the seal when the webbing moves in the opposite direction.

1 3 According to one embodiment of the invention the seal is a bulbous, loosely seated member, having means to bias it into a position retracted from the teeth and means to move it into contact with the teeth on operation of a pretensioner. This avoids normal wear and tear on the stopper and lengthens its life improving the reliability of the system.

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 an enlarged perspective view of a part of a retractor, illustrating the invention.

Figures 2 and 3 are cross-sectional views of a part of the retractor of figure 1.

Many different designs of retractor and of pretensioner may be used in the present invention and such designs will be familiar to persons skilled in this field. For example a retractor as illustrated and described in EP 0 228 729 B. A pretensioner such as described in WO 95/08456 or EP 600 689 A could be used. In general, the retractor will comprise a spool on which seat belt webbing is wound, rotatably mounted so that the webbing can payout or be rewound depending upon the direction of rotation. Sensors are included to detect an impending crash, and to then activate 3 O a locking mechanism to lock the spool against rotation. A pawl which pivots to engage a ratchet wheel attached to the 4 spool is typical.

Figure 1 shows a spool end flange 20 which has teeth 21 on its inner face and is mounted on shaft 22 for common rotation with a spool of a retractor. The spool rotates in direction A to rewind seat belt webbing, for example during a pretensioning operation. The direction B indicates webbing payout.

Pretensioning is effected by a sudden release of gas to drive the spool in the webbing winding direction A. This may be by driving a piston pulling a cable connected to the spool (for example by a clutch which only engages when a pretensioning operation is required). Alternative arrangements are well known and well within the general knowledge of a person skilled in this field. A venting duct 23 for the gas generator (not shown) is arranged in close proximity to the spool end flange 20. The duct has a hole sealed by a stopper 24 which is made of a relatively soft and flexible material. The teeth 21 on the spool end flange 20 are angled so as to present a sloping tooth surface 25 in the belt winding direction A, and a sharp edge 26 in the belt unwinding direction B. Hence as the teeth move past the stopper 24 in the direction A they simply deflect the soft material, whereas when they move past the stopper 24 in the direction B, the sharp edges 26 cut into the soft material and rupture the stopper, allowing gas to escape from the pretensioner. Release of gas from the pretensioner causes a fall in the effective pressure and in the effective pretensioning force exerted on the system. Thus the peak load on the vehicle occupant is limited and the spool can 1 rotate in the payout direction to allow any integral load limiter to function. In this way the pretensioner is decoupled from the load limiter after pretensioning.

In figure 1 the vent stopper 24 is shown in a deployed state in which it is pushed into contact with the teeth 21 on the end flange 20 by the gas pressure. However, under normal use of the retractor, when-there is no gas pressure from the pretensioner, the stopper 24 is pulled back in its mounting in the vent 23 as is shown in figure 2. The stopper 24 has a bulbous shape with a generally U-shaped cross section and an upturned resilient rim 27 which is held in a circular tapering recess 28 in the venting duct 23. With no gas pressure acting on the vent, the vent stopper 24 is pulled back, away from the teeth 21 by the resiliency of the rim 27. When pretensioning occurs, the gas pressure pushes the stopper out, close to the teeth 21, until the rim 27 rests on the forward surface of the recess 28. This is shown in figure 3. The line 29 along which the sharp edges 26 of the teeth 21 will cut the stopper 24 is shown in broken line.

The invention has been described and illustrated in relation to a retractor pretensioner but it could, with 25 minor modification, be extended for use with a buckle pretensioner. For example the locking ratchet wheel might then be replaced by a toothed locking rack, but the arrangement of angled teeth would still apply so that the seal over the gas vent hole remains intact when the rack while pretensioning is being moves in one direction, ie effected, but the seal will be broken to release pressure 6 and limit the load on the occupant when the forward momentum of the occupant is such as to move the rack in the opposite direction.

1 -7

Claims

1. A retractor comprising: a rotatable spool fixedly connected to a toothed ratchet member, a locking pawl for engaging with the ratchet member to lock the spool against rotation in the event of a crash, vent hole for venting gas from a pretensioner, seal for the vent hole, wherein the teeth on the ratchet wheel are asymmetric and are angled so that, in the pretensioning direction of rotation of the ratchet wheel, the teeth present sloping ramp surfaces to the seal, whereas, in the direction of rotation opposite to the pretensioning direction, the teeth present a generally sharp edge substantially toward the seal to rupture it.

2. A retractor according to claim 1 wherein the seal is a bulbous, loosely seated member, and means are provided to bias the seal into a position retracted from the teeth and means are provided to move it into contact with the teeth on operation of the pretensioner.

3. A retractor according to anyone of claims 1 or 2 wherein the pretensioner comprises a piston connected to pull a cable connected to the spool.

A retractor according to claim 3 wherein the cable is connected to the spool via a clutch which only engages when a pretensioning operation is required.

5. A retractor according to anyone of the preceding claims wherein the seal comprises a stopper 24 made of a relatively soft and flexible material.

6. A retractor according to anyone of the preceding claims wherein the sea! has a generally U-shaped cross section and an upturned resilient rim (27) which is held in a circular tapering recess (28) in a venting duct 23.

7. A retractor according to claim 6 wherein the resilient rim (27) is resilient to and forms the means to bias the seal into a position retracted from the teeth.

8. A retractor according to anyone of the preceding claims wherein the ratchet member is a wheel.

9. A retractor according to anyone of claims 1 to 7 wherein the ratchet member is a toothed locking ratchet.

10. An arrangement for venting a pretensioner for a vehicle safety restraint, the arrangement comprising a venting duct connected to a source of pretensioning gas, the duct having a vent hole and a seal for the vent hole, the position of the seal being responsive to the gas pressure, there being means, movable with the seat belt webbing which breaks the seal when the webbing moves in one direction and which does not break the seal when the webbing moves in the opposite direction.

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11. A venting arrangement according to claim 10 wherein the seal is a bulbous, loosely seated member, and means are provided to bias the seal into a position retracted from the teeth and means are provided to move it into contact with the pretensioner.

e teeth on operation of )5 1