GB2323768A

GB2323768A - Safety belt retractor

Info

Publication number: GB2323768A
Application number: GB9706585A
Authority: GB
Inventors: Dan Persson
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 1997-04-01
Filing date: 1997-04-01
Publication date: 1998-10-07
Anticipated expiration: 2017-04-01
Also published as: GB2323768B; GB9706585D0

Abstract

A safety belt retractor comprises two magnetic elements (23, 24) that assist in the retraction of a safety belt. A helical spring provides a first torque that biases a retractor shaft in a winding - in direction. One trunnion of the retractor shaft is formed with a gear wheel (21) that engages an internally toothed gear ring (22). A magnet (23) carried by the gear ring (22) is brought adjacent to a fixed magnet (24) when the safety belt is almost completely wound onto the shaft. The resultant magnetic attraction provides an additional torque to the shaft to complete the winding - in process. In an alternative embodiment a wire is paid out from the retractor as the belt is wound in and a magnet on the wire is attracted by a fixed magnet.

Description

Agents Ref: P11302GB-NHF/sd Title: Improvements In Or Relating To A Safety Belt Retractor THE PRESENT INVENTION RELATES TO a safety belt retractor and more particularly relates to a safety belt retractor utilized to retract a safety belt provided in a motor vehicle such as a motor car.

Most conventional safety belt retractors utilize a helical spring or clock spring, connected between a spool on which the safety belt is wound, and a housing in which the retractor mechanism is contained, to wind up the belt onto the spool. A spring of this type gives a substantially constant torque, but because the diameter of the belt wound on to the spool is much larger when the belt is full retracted, as compared to when the belt is in use, the retraction force is much smaller in the final stages of retraction than when the belt is substantially withdrawn from the retractor.

In order to provide sufficient retraction force at the end of the retraction it is, of course, possible to increase the torque provided by the spring. However, this provides a very high tension in the belt when the belt is in use, which can be very uncomfortable. Consequently, a relatively low torque is preferable for the spring, meaning that insufficient retraction force may be provided during the final stages of the retraction process.

It has been proposed previously to overcome this difficulty by utilizing a mechanical switch gear to connect a second stronger spring to the spool for the final stages of retraction of the belt. Such a second spring must be disconnected from the spool after a certain amount of webbing has been paid out. An arrangement of this type has been found to be relatively clumsy.

Another prior proposal utilized a continuously variable gear between the spring and the spool. This is also a very clumsy solution to the problem.

According to this invention there is provided a retractor mechanism for a safety belt comprising a housing, a spool mounted for rotation relative to the housing having one end of a safety belt wound thereon, a spring connected between the spool and the housing to provide a rotational bias to the spool to retract the belt onto the spool, and co-operating magnetic elements, one said magnetic element being mounted in a fixed position and the other said magnetic element being adapted to move in response to movement of the spool, the arrangement being such that as a safety belt is retracted onto the spool, the moveable magnetic element moves towards the fixed magnetic means so that there is attraction between the magnetic elements thus applying an additional torque to the spool to facilitate the completion of the retraction procedure.

Preferably the magnetic elements comprise at least one permanent magnet.

Alternatively the magnetic elements comprise two permanent magnets.

Conveniently the moveable magnetic element is adapted to effect a rotational movement.

Preferably a gear wheel is provided adapted to rotate on rotation of the shaft, the gear wheel being of a predetermined diameter and being associated with a gear ring of a larger diameter, the gear ring having an inner periphery which is toothed and which engages the toothed periphery of the gear wheel, the gear ring carrying the movable magnetic element.

Preferably the gear ring carries radially outwardly extending arm which in turn carries a substantially tangentially directed finger, said finger comprising the movable magnetic element.

In an alternative embodiment of the invention the movable magnetic element is mounted for linear movement.

Conveniently the movable magnetic element is connected to a long flexible element which is wound round a member, which rotates on rotation of the spool, in such a sense that the movable magnetic element is moved towards the fixed magnetic element when the belt is retracted into the retractor mechanism.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a graphical figure illustrating the torque applied to a safety belt as compared with the length of safety belt pulled out from a retractor reel, illustrating both a conventional reel and a reel in accordance with the invention, Figure 2 is a cross sectional view of a retractor reel in accordance with the invention, Figure 3 is a sectional view taken on the line III III of figure 2, Figure 4 is a sectional view taken on the line IV IV of figure 2, Figure 5 is a scrap sectional view of an alternative embodiment of the invention, and Figure 6 is a diagrammatic sectional view of a further alternative embodiment of the invention.

Referring initially to figure 1 of the accompanying drawings, the length of safety belt, 1, pulled out from a retractor reel is plotted against the retractive torque, T, applied to the spool. As the belt is pulled out as shown in point 1 on the graph, a substantially constant torque is applied to the spool, this torque rising, 2, towards the end of the retraction process. When the belt is released and retracted back onto the reel, a somewhat lower torque, 3, is achieved, due to the effect of friction.

It can be seen that over a substantial proportion of the retraction, as indicated by the double headed arrow 4, there is a substantially constant torque. During the final stages of retraction, as indicated by the double headed arrow 5, the torque is constant but because of the large diameter of the spool of belt, wind up may not be accomplished in a desired manner.

Referring now to figure 2 of the accompanying drawing, the essential parts of a retractor mechanism in accordance with the invention are illustrated. The retractor mechanism comprises a shaft or spindle 10, having projecting trunnions 11, 12, which are received in corresponding apertures provided in support frame elements 13, 14. The shaft 10 carries a spool 15 in which is wound, in a helical manner, a seat belt 16. A helical or clock spring 17 is provided having one end 18 connected to the trunnion 11 and the other end 20 connected to the housing 13, to provide a rotational bias to the spool tending to wind the seat belt 16 onto the spool.

A portion 19 of the seat belt emerges from the housing.

As thus described, the retractor mechanism is conventional.

As can be seen in figures 2 and 4, formed on the trunnion 11 is a gear wheel 21. The gear wheel 21 is of relatively small diameter and has a toothed outer periphery.

A gear ring 22 is provided which is associated with the gear wheel 21. The gear ring is of greater diameter than the gear wheel 21, and has a toothed interior, the toothed interior of the gear ring 22 meshingly engaging with the gear wheel 21. A magnet 23 is provided which is mounted on the exterior of the gear ring 22. A second magnet 24 is provided which is mounted in a fixed position.

In the condition illustrated the magnet 24 is immediately adjacent the magnet 23, with the magnet 24 having a south pole adjacent to the north pole of the magnet 23. The magnets thus attract each other.

It is to be appreciated that the retractor mechanism will have the condition illustrated when the safety belt 16 is substantially completely retracted onto the spool 15. In this condition the magnet 23 is attracted to the magnet 24. This tends to impart a rotational bias to the gear ring 22 which tends to impart a corresponding rotational bias to the gear wheel 21 which in turn biases the shaft and the spool 15. Thus an additional torque is applied to the spool by the effect of the magnets 23 and 24. This torque combines with the torque provided by the spring 17 to assist in the completion of the retraction of the safety belt. This added torque is shown at line 25 in figure 1.

When the safety belt is paid out, the spool 15 is rotated in such a direction that the gear ring 22 will be rotated in a direction so as to move the magnet 23 away from the magnet 24. Thus, the torque that has to be overcome on the initial withdrawal of the safety belt is somewhat higher than in a conventional safety belt, as shown by line 26 in figure 1. However, once the initial withdrawal of the safety belt has been accomplished the magnet 23 will be moved so far away from the magnet 24 that there will effectively be no magnetic coupling between the magnets. Thus, during the part of retraction identified by the double headed arrow 4 in figure 1, the retractor mechanism illustrated in figures 2 to 4 will again provide a substantially constant torque.

Figure 5 illustrates a slightly modified embodiment of the invention in which a gear wheel 31 mounted on a trunnion of the spool co-operates with a gear ring 32. The gear ring 32 carries an outwardly directed arm 33 which in turn carries a projecting arm 34 that extends substantially tangentially. The arm 34 is dimensioned to be received in the interior of a magnetic housing 35. The arm 34 may be made of a magnetic material such as soft iron, and it is to be understood that the magnetic housing 35 will attract the arm 34, thus applying a force to the arm 34 whilst the arm 34 is in the vicinity of the magnetic housing 35.

Thus the embodiment of figure 5 will provide a very similar effect as that of the embodiment of figure 4, since when the belt is almost fully wound onto the spool, the arm 34 will be brought close to the magnetic housing 35, and the resultant attraction will provide a force which assists in the completion of the retraction process.

Figure 6 illustrates another embodiment of the invention in which a wire or cord 41 is provided which is adapted to be wound onto the trunnion 11 as the spool rotates. The sense of winding on the trunnion 11 is such that the cord or wire 41 is unwound from the trunnion 11 when the seat-belt is retracted onto the spool. The cord or wire 41 carries, at its lower end, as illustrated, a magnet 42, and there is a fixed magnet 43 which is secured in an appropriate position. The magnet 42 may be constrained to follow a linear path. When the seat-belt has been substantially completely retracted onto the spool 15, a sufficient length of cord or wire 41 has been paid out for the magnet 42 to be located immediately adjacent to the magnet 43. The polarity of the magnets is such that there is a mutual attraction between the magnets, and thus as the magnet 42 approaches the magnet 43 a substantial force is applied to the cord or wire 41, thus assisting the torque applied to the spool by the spring 17, facilitating completion of the retraction procedure.

Claims

CLAIMS:

1. A retractor mechanism for a safety belt comprising a housing, a spool mounted for rotation relative to the housing having one end of a safety belt wound thereon, a spring connected between the spool and the housing to provide a rotational bias to the spool to retract the belt onto the spool, and co-operating magnetic elements, one said magnetic element being mounted in a fixed position and the other said magnetic element being adapted to move in response to movement of the spool, the arrangement being such that as a safety belt is retracted onto the spool, the moveable magnetic element moves towards the fixed magnetic means so that there is attraction between the magnetic elements thus applying an additional torque to the spool to facilitate the completion of the retraction procedure.

2. A retractor according to claim 1 wherein the magnetic elements comprise at least one permanent magnet.

3. A retractor according to claim 2 wherein the magnetic elements comprise two permanent magnets.

4. A retractor according to any one of the preceding claims wherein the moveable magnetic element is adapted to effect a rotational movement.

5. A retractor according to claim 4 wherein a gear wheel is provided adapted to rotate on rotation of the shaft, the gear wheel being of a predetermined diameter and being associated with a gear ring of a larger diameter, the gear ring having an inner periphery which is toothed and which engages the toothed periphery of the gear wheel, the gear ring carrying the movable magnetic element.

6. A retractor according to claim 5 wherein the gear ring carries radially outwardly extending arm which in turn carries a substantially tangentially directed finger, said finger comprising the movable magnetic element.

7. A retractor according to any one of claims 1 to 3 wherein the movable magnetic element is mounted for linear movement.

8. A retractor according to claim 7 wherein the movable magnetic element is connected to a long flexible element which is wound round a member, which rotates on rotation of the spool, in such a sense that the movable magnetic element is moved towards the fixed magnetic element when the belt is retracted into the retractor mechanism.

9. A retractor mechanism substantially as described with reference to and as shown in figures 2 to 4 of the accompanying drawings.

10. A retractor mechanism substantially as described with reference to and as shown in figures 2 to 4 of the accompanying drawings as modified by figure 5.

11. A retractor mechanism substantially described with reference to and as shown in figures 2 to 4 of the accompanying drawings as modified by figure 5.

12. A retractor mechanism substantially described with reference to and as shown in figures 2 to 4 of the accompanying drawings as modified by figure 6.

13. Any novel feature or combination features disclosed herein.