GB2347650A

GB2347650A - Seat belt retractor

Info

Publication number: GB2347650A
Application number: GB9905514A
Authority: GB
Inventors: John Bell; Frederic Jallot; Michael Thwaite; David Burke
Original assignee: Breed Automotive Technology Inc
Current assignee: Breed Automotive Technology Inc
Priority date: 1999-03-10
Filing date: 1999-03-10
Publication date: 2000-09-13
Also published as: GB9905514D0

Abstract

A retractor for a vehicle seat belt comprises a spool 8, mounted for rotation about its axis and having seat belt webbing wound thereon, a crash sensor responsive to changes in conditions indicative of a crash condition, and a friction braking device 11 responsive to the crash sensor and movable, into a position in which it applies a friction braking force to the spool 8 to lock it. The friction braking device 11 may operate directly on the spool 8 or through an intermediate part. A controller may be provided to control the braking force and the time taken to fully brake the spool 8.

Description

RETRACTOR DESCRIPTION The present invention relates to a retractor for a vehicle safety restraint seat belt.

A seat belt retractor typically comprises a spool on which seat belt webbing is wound and which is spring biased to the webbing retracted condition to maintain a tension on the belt around a restrained vehicle occupant. Under normal driving conditions the spool is otherwise free to rotate to pay out more webbing as the occupant moves in the seat: for example to reach dashboard controls. However the retractor is normally fitted with both a web sensor and a vehicle sensor. The web sensor detects when belt webbing is suddenly jerked, as would happen if it were suddenly loaded by the forward momentum of the occupant in a crash for example. This is known technology. The vehicle sensor detects a sudden change of speed of the vehicle, again as would occur during a crash. In both cases the sensor serves to lock the spool against further protraction of webbing so as to securely restrain the occupant against further forward movement. Again, this is known to those skilled in the art.

In a traditional retractor the spool is locked, in a crash situation, by load bearing locking members, responsive to the sensors, moving into positions in which they interlock the spool to a fixed part of the vehicle, either directly or indirectly. For example, in one such known retractor, a load bearing locking dog or pawl is connected at its pivot point with the frame of a retractor and is movable into a position in which the end of the pawl engages a toothed ratchet wheel connected to the webbing spool. In a crash this pawl is moved to engage the ratchet wheel and hence lock the spool to the retractor frame and hence to the vehicle load bearing pillar to which the retractor frame is mounted.

Problems arise with this traditional locking mechanism unless the locking engagement is properly phased. At high loads an incorrectly phased locking action can cause teeth on the ratchet wheel to shear, or the locking pawl to bounce off the teeth, and the spool will not be efficiently locked as a result. Servomechanisms can be used to ensure correct phasing but this increases the complexity and consequently the cost of the retractor. It is important to keep the cost minimised whilst ensuring reliability of the retractor. In addition, in a traditional retractor there is always a residual pay out of webbing after the crash sensor has been activated due to the spacing of the ratchet teeth since the spool can only be locked at incremental intervals corresponding to the spacing of the teeth on the ratchet wheel. This is undesirable and potentially dangerous. It can be reduced by decreasing the spacing of the teeth but evidently this increases costs and can introduce problems with tolerances and with strength.

It is an object of the present invention to provide an improved retractor.

According to the present invention there is provided a retractor comprising a spool, mounted for rotation about its axis and having seat belt webbing wound thereon, a crash sensor responsive to changes in conditions indicative of a crash condition, and a friction braking device responsive to the crash sensor and movable, in response to a signal from the crash sensor, into a position in which it applies a friction braking force to the spool to lock it against further webbing protraction.

Preferably the friction braking device comprises a friction braking tongue. The friction braking device may be arranged to act directly on the spool, for example on the side of the spool or on the end thereof. Alternatively it may be arranged to act indirectly on the spool, for example by applying a friction braking force to an intermediate member with may act directly to lock the spool against further webbing pay out. The friction device may also be arranged to be actuated by a servomechanism using the load or part of the load applied to the webbing (by the momentum of the vehicle occupant in a crash situation).

According to a preferred embodiment of the present invention there is provided means for controlling the friction braking device so as to control the braking profile, for example the initial braking force applied, and the time taken to bring the spool to its fully braked and stationery position. A retractor constructed according to this preferred embodiment could form the basis of a load limiting retractor system which can cushion some of the initial load felt by the restrained occupant during a crash and spread it over a longer time period. This is more comfortable for the occupant and serves to reduce injuries caused by the seat belt restraint itself particularly during a high speed, or high load, crash.

Another advantage of a retractor according to the invention is that the performance of the locking mechanism is not related to the spacing of the ratchet teeth. The spool locking begins immediately the friction device is moved to contact the spool.

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 retractor according to one embodiment of the invention, as seen from one side; Figure 2 is a view from the other side of the retractor of Figure 1 ; Figure 3 is a cross-sectional view from the back of the retractor of Figure 1 ; Figure 4 is a cross-sectional view from the side of the retractor of Figure 1 ; Figure 5 is a perspective view from the side of a retractor according to a second embodiment of the invention.

In the Figures like parts are indicated by like reference numbers. A retractor frame is indicated at 1 comprising a generally U-shaped load bearing metal structure which can be fitted to a fixed part of a vehicle. Typically the frame would be fixed to the pillar of a vehicle by means of a bolt passing through a fixing hole 2 formed in the back 3 of the frame 1. In each of the side walls 4 and 5 a large generally circular hole 6 and 7 respectively is formed. A cylindrical spool 8 is supported on its axis 9 to bridge the space between the side walls 4 and 5 of the frame 1 between the holes 6 and 7. In use, seat belt webbing is wound on the spool 8 but is not shown in the illustrations.

On the side 4 of the frame 1 there is a cutout 10 which laterally extends the hole 6. A braking member 11, of generally triangular shape is supported in this cutout 10 and is mounted for sliding movement towards and away from the corresponding end of the spool 8 by means of a tab 12 on the braking member 11 which fits into a slot 13 in a cross bar 14. The cross bar 14 is fixed to the axis 9 of the spool and to the side 4 of the frame 1 by bolt or rivet 15. The face of the braking member 11 which faces the spool 8 is coated with a high friction material or coating so as to grip the side of the spool 8 efficiently and apply a good braking force to it when required.

One or more crash sensors (not shown) are arranged to control the braking member 11 so as to move it into frictional engagement with the spool 8 when a crash condition is sensed. This may be for example by connection of the crash sensor to the tab 12 in such a way as to slide the tab 12 and hence the braking member 11 towards the spool. The braking member 11 may be resiliently biased away from the spool so as to ensure unhindered rotation of the spool under normal (non-crash) operating conditions.

Figures 1 to 4 show different views of the same embodiment of the invention. In this embodiment, part of the load is applied directly on the webbing.

Figure 5 shows a different embodiment of the invention in which the braking member 11 in cutout 10 is situated below the spool 8 instead of at the side of it. The cross bar 14 is not shown in this Figure and of course may be replaced by some other form of support for the braking member 11. Otherwise the operation of the embodiment of Figure 5 is identical to the operation of the embodiment of Figures 1 to 4.

Claims

1. A retractor comprising a spool, mounted for rotation about its axis and having seat belt webbing wound thereon, a crash sensor responsive to changes in conditions indicative of a crash condition, and a friction braking device responsive to the crash sensor and movable, in response to a signal from the crash sensor, into a position in which it applies a friction braking force to the spool to lock it against further webbing protraction.

2. A retractor according to claim 1 wherein the friction braking device comprises a friction braking tongue.

3. A retractor according to claim 1 or claim 2 wherein the friction braking device is arranged to act directly on the spool.

4. A retractor according to claim 3 wherein the friction braking device is arranged to act directly on the side or on the end of the spool.

5. A retractor according to claim 3 wherein the friction braking device is arranged to act indirectly on the spool.

6. A retractor according to claim 3 wherein the friction braking device is arranged to apply a friction braking force to an intermediate member which is arranged to act directly to lock the spool against further webbing pay out.

7. A retractor according to any one of the preceding claims further comprising a servomechanism arranged to use at least part of the load applied to the webbing by the momentum of the vehicle occupant in a crash situation to actuate the friction braking device.

8. A retractor according to any one of the preceding claims comprising means for controlling the friction braking device so as to control the braking profile.

9. A retractor according to claim 8 wherein the controlling means is arranged to control the initial braking force applied, and the time taken, to bring the spool to a fully braked and stationery position.

10. A retractor according to claim 9 forming a load limiting retractor.

11. A retractor substantially as hereinbefore described with reference to the Figures 1 to 4 or Figure 5 of the accompanying drawings.