GB2346849A - Seat belt retractor with force limiting means - Google Patents

Abstract

A seat belt retractor comprises: a spool 1 mounted on a shaft 10 for rotation; a length of seat belt webbing 22 wound on the spool for retraction or pay-out; means for locking the spool shaft against rotation when a crash condition is sensed; and force limiting means for allowing further pay-out of the webbing after the spool has locked. The force limiting means comprises an energy absorbing arrangement connecting the spool to the spool shaft by means of a deformable tube 24 mounted on the spool shaft and means for applying a compressive load to the tube when a high load is applied to the retractor. The compressive load may be applied by means of a nut 26 rotatably mounted on the spool shaft. A bearing disc 25 may be provided which rotates with the spool and substantially removes torque from the deformable tube. The force limiting means is intended to reduce excessive forces applied to the occupants body during a vehicle impact.

Description

2346849

RETRACTOR SPOOL DESCRIPTIO

This application is divided from GB 97 01 443.5 and is related to copending divisional application GB 00 11285.4 The present invention relates to a retractor spool for a vehicle safety restraint.

A retractor spool generally consists of a cylindrical bobbin with a circular cross-section. Seat belt webbing is attached to and wound around the spool and the spool is mounted on a spool shaft to be rotatable in the retractor to wind in webbing under action of a retractor spring and to pay out webbing under the influence of relatively gentle forwardly directed inertia of a vehicle occupant, for example to allow for normal movement associated with vehicle occupancy such as reaching forwards to activate in-car controls (for a radio or a window) or to reach a glove compartment or door pocket. In the event of a crash situation, the more extreme momentum of the occupant activates a crash sensor which locks the spool against rotation and thus prevents forward motion of the occupant and injury due to occupant collision with the interior fixtures of the vehicle such as the steering wheel, dashboard or windscreen.

However, this sudden locking of the seat belt spool under crash conditions can itself sometimes cause injury to the occupant due to sudden impact of the tcrso with the belt webbing. This is particularly true in high velocity -2crashes.

In recent years this problem has been recognised and some solutions proposed.

one solut-Lon has been to rely on natural elongation of the webbing under high loads, and on the spool film effect (natural tightening of the webbing wound on the spool under high loads), to produce a load limiting effect.

Another known proposal has been described in EP 0 297 537 A, wherein force limiting is effected by interposing a plastically deformable member between the spool and the innermost winding of the belt webbing or by interposing an elastic member such as a spring rubber member or resin member between an end flange of the spool and the latch plate. This allows a pay-out of webbing in proportion to the inertia of the vehicle occupant at the moment of a crash condition being sensed. This pay-out lessens the otherwise severe restraining forces on the occupant at high vehicle speeds especially during the initial moments of the crash. It thus reduces the injurious effects of the seat belt in a crash.

The present invention proposed improved load limiting arrangements for retractors.

According to the present invention there is provided a seat belt retractor comprising a spool mounted on a spool shaft for rotation in the retractor,a length of seat belt webbing wound on the spool for retraction or pay-out depending on the rotation direction of the spool; means for locki-.ng the spool shaft against rotation when a crash condition is sensed; force limiting means for allowing further pay-out of the seat belt webbing after the spool shaft has locked, under the influence of an occupant's forward momentum in the crash condition, wherein the force limiting means comprises an energy absorbing arrangement connecting the spool to the spool shaft, the connection being rigid below a predeterm-L-ned force, and above the predetermined force there being relative rotation of the spool with respect to the spool shaft to allow pay out of belt webbing, and wherein the energy absorbing member of the force limiting means comprises a deformable member comprising an axially outwardly deformable crushable tube mounted on the rotation shaft of the spool and wherein means are provided for applying a compressive load to the crushable tube axially of the spool when a high load is ap-olied to the retractor under crash -- cnditions.

The deformable member may be a crushable or deformable tube. The tube may be mounted on the shaft at one end of the spool, or within a hollow spool.

Preferably the deformable tube is deformable outwardly in a radial direction under an axial compressive load, for example, one end may splay radially outward or the middle region of the tube may bulge outward.

The compressive load may be applied by a nut abutting the deformable tube and mounted on the spool shaft, and which rotates to apply force to the deformable tube when a high crash load is detected. It can also be adjusted by the pitch_ and type (e.g. square or sinusoidal) of the threading on the bolt and nut.

According to a preferred embodiment the maximum and minimum levels of load limiting are definable. This may be achieved by a suitable choice of material, shape and size of the deformable tube.

Preferably a bearing disc is provided to rotate with the spool and substantially remove torque from the crushable tube member. This gives a more predictable load limiting curve.

This load limiting arrangement may be used with a single-sided locking retractor, or with a double-sided locking retractor.

Double-sided locking may be achieved by lock dogs at each end of the retractor connected by a rctatable shaft. Preferably however it is achieved by building in a controlled amount of compliance at the mechanical end of the spool and using relative rotation of the spool relative to the spool shaft during load limiting to lock the other end of the spool, which for example would be the pretensioner end in a retractor where a pretensioner is fitted.

Th 4 s avo L the long tJ e bar otherwise needed to connect two lock doas for double-sided locking and improves 3 the webbing capacity of the spool.

The invention is particularly applicable to the load limiting retractor known as the constant force retractor and described in co-pending International application PCT/US95/15002, publication WO 96/16843.

When a pretensioner is fitted it is preferably to avoid the pretensioner loads being transmitted through the load limiter. This can be achieved using shear pins connecting the spool to the ratchet at the spool mechanism end. During load limiting the shear pins break and bring a clutch into engagement for the pretensioner. This ensures that the pretensioning load applied to the belt is less than the load limiter threshold.

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 I is a cross-sectional schematic view of a retractor according to a first embodiment of the present invention; Figures 2 and 3 are schematic views to the left (pretensioner) side and the right (mechanism) side respectively of the retractor of Figure 1; Figure 4 is a graph of force against time for the load limiting retractor of Figures 1 to 3; Figure 5 shows a second embodiment- of a load limiting retractor of the present invention; Figure 6 is an enlarged view of part of Figure 5; Like parts are denoted by like reference numerals 5 throughout.

Figures 1 to 3 show a retractor with spool I on which is wound belt webbing 22 and which is rotatably mounted on a shaft 10. A load limiter member in the form of a deformable hollow cylindrical tube 24 is mounted on shaft 10 between a bearing disc 25 and a nut 26 which is also mounted about shaft 10.

Rotation of the spool after it is locked, to prevent further webbing pay out in response to a crash sensor, causes nut 26 to rotate on the shaft 10 and move towards the hollow tube 24, thus compressing it between the bearing disc 25 and the nut 26. In Figure I the tube 24 is shown in a compressed form being bulbous. The bearing disc 25 rotates with the spool and thus removes all torque from the crushable member, giving a more predictable performance.

Figure 3 illustrates a main ratchet wheel 27 at the right hand (mechanism end) of the spool 1. Teeth 28 on the outer circumference of the main ratchet wheel 27 are engaged by a locking pawl when a crash situation is indicated to lock the right hand side of the spool 1. wheel spokes 29 are constructed to deform under a predetermined load as shown in Figure 3a, allowing torque to be transferred to the 3'0 other end (spring side) of the spool 1, allowing locking teeth at the other end to engage and share the locking -7torque.

Figure 2 illustrates the spring side of the spool 1 and shows spaced locking bars 30 mounted in carrier plate 31.

During load limiting the relative motion between the spool i and the lockbar carrier plate 31 pushes the lockbars 30 radially outwardly to engage teeth on the retractor frame (not shown). This locks the left hand side of the spool 1 and thus the spool is locked securely at both sides aft-e-r 10 load limiting.

The sequence of operation is shown by the graph of Figure 4 where line I represents the load on the main ratchet (mechanism side) and line II that on the secondary ratchet (spring side).

At the onset of the crash situation, the spool I is locked at A. As the load on the webbing increases due to the inertia of the vehicle occupant, the webbing is pulled tighter on the spool. This is known as cinching and is shown on the graph at B. When the webbing is fully tightened on the spool, the load transfers to the spool; and the load limiter comes into effect at C taking all the load on the main ratchet. At D the load limiter bottoms out and the main ratchet yields transferring some load to the other end of the retractor. The load on the secondary ratchet thus increases at this stage while that on the main ratchet remains fairly constant at E.

Fiaure 5 shows an alternative load limiting member in the form of a hollow conical tube 24. Like parts are denoted by like reference numerals and the function of the arrangement is identical to that for the arrangement oif Figures 1 to 3. The hollow conical tube 24 expands radially when an axial force is applied. The sha- oe of the conical 5 tube 24 of Figure 5 is shown in greater detail in Figure 6.

The sequence of operation of this arrangement with a pretensioner will now be described.

when pretensioning begins, the spool 1 and the mechanism end main ratchet 27 are connected by shear pins and the ratchet 27 is locked by engagement with a lockbar (not shown).

As the pretensioner force increases, the shear pins break and the load limiter operates. All the load is at the mechanism end on the main ratchet 27 and the spring side (left hand side in Figure 1) lockbars 30 are not engaged with the frame although they are driven outwards towards the frame.

when load limiting ceases the load on the spool increases causing deformation of the spokes 29 of the main ratchet 27. This allows the spring end locking bars 30 to contact the frame thus completing double-sided locking with a controlled sharing of the load between the two ends of the spool.

The construction of the spring side locking system (locking bars 30) can be varied to either maintain the spool locked after the pretensioning stroke, or to release it to run freely, as desired.

Claims (3)

1. A seat belt retractor comprising a spool mounted on a spool shaft for rotation in the retractor, a length of seat belt webbing wound on the spool for retraction or pay-out depending on the rotation direction of the spool; means for locking the spool shaft against rotation when a crash condition is sensed; force limiting means for allowing further pay-out of the seat belt webbing after the spool shaft has locked, under the influence of an occupant's forward momentum in the crash condition, wherein the force limiting means comprises an energy absorbing arrangement connecting the spool to the spool shaft, the connection being rigid below a predetermined force, and above the predetermined force there being relative rotation of the spool with respect to the spool shaft to allow pay out of belt webbing, and wherein the energy absorbing member of the force limiting means comprises a deformable member comprising an axially outwardly deformable crushable tube mounted on the rotation shaft of the spool and wherein means are provided for applying a compressive load to the crushable tube axially of the spool when a high load is applied to the retractor under crash conditions.

2. A seat belt retractor according to claim 1 wherein the compressive load is applied by a nut abutting the crushable tube and mounted on the spool shaft, and which rotates to apply force to the crushable tube when a high - I I - crash- load is applied, the retractor comprising a bearing disc -mounted to rotate with the spool and substantially remove torque from the crushable tube member.

3. A seat belt retractor according to claims 1 or 2 when used with a double-sided locking retractor.