GB2154853A - Vehicle seat belt retractor - Google Patents

Abstract

The retractor has a spool 15 rotatable on a shaft 8 non-rotatably secured to end plates 2, 4 of the retractor frame. The spool 15 has cup-shaped end-portions 22, 24 which house the retractor spring (not shown) and part of a belt- sensitive locking mechanism 41 etc. (see also Fig. 2). The retractor spring is received in a housing 26 and its inner end engages a square end portion 9 of the shaft. In manufacture, the spring and housing are pre-assembled before they are fitted to the spool, the spool is then positioned in the frame and the shaft inserted to mount the spool and secure the spring. The locking mechanism includes a pawl member having toothed portions 34 which engage teeth 25 on the cup-shaped spool portions. A vehicle-sensitive locking mechanism includes a ball 72 on a conical seat 70. The orientation of the seat can be adjusted by rotation on orthogonal pivots 66, 68, the axes of which pass through the centre of the ball. An output pawl 62 of the mechanism engages the teeth 25 to initiate locking and is operated by an intermediate pivoting member 74. <IMAGE>

Description

SPECIFICATION Seat belt retractor The invention relates to a vehicle seat belt retractor.

More specifically the invention relates to the type of vehicle seat belt retractor which comprises a spool having an end of a seat belt secured thereto, a frame having spaced apart portions rotatably supporting the spool therebetween, a retractor spring biassing the spool to rotate to wind the belt thereon and a locking mechanism arranged to lock the spool against belt protraction in response to a predetermined condition.

Prior art retractors of this type are in general complicated so as to present difficulties in the manufacture of parts and in assembly.

They tend also to be bulky and left- and righthanded, so that modification of a basic design may be needed where the space in the vehicle available for the retractor is limited.

The present invention is accordingly concerned with the provision of a vehicle seat belt retractor which can be simply produced and which is also compact and symmetrical about a plane bisecting the portion of the spool on which the belt is coiled.

The invention accordingly provides a vehicle seat belt retractor of the type mentioned in which the spool has an end of a seat belt secured thereto, a frame having spaced-apart portions between which the spool is rotatably supported, a retractor spring biassing the spool to rotate to wind the belt thereon and a locking mechanism arranged to lock the spool against belt protraction in response to a predetermined condition, in which the spool has a lesser cross-section portion on which the belt is wound and a portion of greater crosssection which has locking formations thereon and which axially overlaps at least a part of the retractor spring or locking mechanism.

The spool can thus be provided with a cuplike portion at at least one end which partially or completely receives the spring or the locking mechanism, typically comprising inertial means responsive to one or both of a predetermined acceleration of the belt in the withdrawal direction and a predetermined acceleration of the retractor itself. The cup-like end portion can be provided with external ratchet teeth engageable with a locking pawl. Preferably, the spool has two cup-like end portions for the spring and the mechanism respectively, to facilitate obtaining a symmetrical form of the retractor, and preferably each such portion has the external ratchet teeth.

Because of the overlapping of the spool locking formation and the spring and/or the locking mechanism, a small retractor dimension axially of the spool can be obtained. Additionally, because the ratchet teeth of the spool end portion or portions can have a considerable axial extent, the load experienced in use is correspondingly distributed. A like advantage can be obtained also by providing the cooperating pawl member or members with a plurality of teeth.

Preferably the locking mechanism includes a rotatably-mounted inertia member which is housed in an axially-overlapping portion of the spool, the inertia member being arranged to rotate with the spool at spool accelerations below a predetermined threshold value and to lag relative thereto at accelerations equal to or exceeding the threshold value, an operating member which is operatively connected to the locking member and which has a cylindrical portion which extends around the inertia member and is at least partially housed in the said axially-overlapping spool portion, and means for coupling the inertia member and the cylindrical operating member portion for joint rotation of the inertia and operating members when the inertia member lags relative to the spool, the operating member upon such rotation causing movement of the locking member from its first to its second position.

The coupling means may comprise a pawl member pivotally mounted adjacent the inertia member and ratchet teeth on the cylindrical operating member portion engageable with the pawl member to effect coupling, the pawl member having an integral resilient portion which is in engagement with the inertia member and deforms resiliently when the pawl member pivots to engage the ratchet teeth.

Otherwise, the coupling means can comprise a pawl member pivotally mounted adjacent the inertia member and ratchet teeth on the cylindrical operating member portion engageable with the pawl member to effect coupling, the pawl member being biassed by a resilient means into sliding contact with the periphery of the inertia member and the point of contact moving outwardly from the spool axis when the inertia member lags relative to the spool.

In some preferred embodiments, an axiallyoverlapping portion of the spool overlaps the retractor spring which is housed in the overlapping portion by a closure member having an end wall which extends transversely to the spool axis to close an open end of the overlapping portion.

Advantageously, the spool of the retractor specified in the fifth paragraph of this specification has an axial bore and is rotatably supported on a shaft extending between the spaced apart portions of the frame and the invention also provides a vehicle seat belt retractor comprising a spool having an end of a seat belt secured thereto, a frame having spaced-apart portions between which the spool is rotatably supported, a retractor spring biassing the spool to rotate to wind the belt thereon and a locking mechanism arranged to lock the spool against belt protraction in re sponse to a predetermined condition, in which the spool has a bore and rotates on a shaft passing through the bore and extending be tween the spaced-apart portions of the frame.

Mounting the spool in this way eliminates the need to provide separate bushes or the like at the two ends of the spool.

The invention also provides a method of assembling a seat belt retractor of the type described, the method comprising the steps of connecting the outer end of the retractor spring to the spool at a position radially spaced from the spool axis, the spring being in a wound condition, inserting a shaft into an axial bore of the spool and into engagement with the inner end of the spring and locating an end portion of the shaft non-rotatably in an aperture in a spaced portion of the frame to secure the inner end of the spring against movement relative to the frame.

Advantageously, the shaft is inserted into the spool bore after alignment of the bore with respective apertures in the spaced portions of the frame.

The assembly method can be one in which the shaft has a cup-like end portion and, before fitting to the spool, the spring is held in its wound condition in a housing receivable in the cup-like end portion, the spring and housing then being inserted into the end portion prior to insertion of the shaft into the spool bore and the inner end of the spring being located in the housing in a position in which it is engaged by the shaft.

Such assembly methods permit the use of a prewound spring so that problems associated with winding after assembly are avoided.

The retractor assembled in accordance with this method necessarily has the shaft fixed against rotation with the spool rotating on it.

The invention also provides a vehicle seat belt retractor of the type described having an inertial retractor acceleration sensing device laterally spaced from the spool, the device comprising a support for an inertial body permitting displacement of the body from a rest position in response to a predetermined retractor acceleration, a locking lever pivotable to lock the retractor against belt protraction in response to such displacement, and means mounting the support for selective rotation about at least one axis extending substantially through the centre of gravity of the body, to maintain the body normally in its rest position over a range of orientations of the retractor without substantial change in the operative relationship between the body and the locking lever.

The support can be mounted in a variety of ways and various arrangements can be adopted to apply movement of the inertia body from its rest position to effect pivotation of the locking lever over the possible range of adjustment of the support within the retractor.

The support can pivotably mount an output lever having an output surface engaging the locking lever which surface is substantially centred on the centre of gravity.

The locking lever can however rest directly on the inertial body, the selective movement of the support being obtained by means of a part spherical surface on either the support or the mounting means therefor, or both, which is substantially centred on the centre of gravity of the inertial body.

Conveniently, the inertial body comprises a ball resting on a frusto-conical surface of the support.

An embodiment of the invention is described below by way of illustration, with reference to the accompanying drawings, in which: Figure 1 is a front view of a retractor embodying the invention, with a cover removed and certain parts omitted.

Figure 2 is a partial sectional side view of the retractor of Fig. 1; Figure 3 is a partial sectional side view taken on the line Ill-Ill of Fig. 1; Figure 4 is a partial front view of a pawl member included in the retractor of Fig. 1; Figures 5 and 6 are partial schematic side views of a modified form of a belt sensitive inertial acceleration sensing device included in the retractor of Figs. 1 to 4, in respective different conditions; Figures 7, 8 and 9 are partial, side, front and plan views respectively of a modified form of a vehicle sensitive inertial accleration sensing device included in the retractor of Figs. 1 to 4; and Figure 10 is a partial front view of a second mofieid form of the vehicle sensitive inertial acceleration sensing device of the retractor of Figs. 1 to 4.

The illustrated retractor comprises a channel-shaped rigid metal frame 1 having parallel side walls 2, 4 joined by a central wall 5 apertured at 6 to receive an anchorage bolt.

The retractor is received in use in a cover (not shown) which may be of plastics material designed to make a snap fit over the frame.

A steel shaft 8 extends through aligned apertures 9, 10 in the side walls 2, 4 respectively. The shaft 8 is circular in cross-section over the major portion of its length, but has a reduced square cross-section end portion 11 received in the aperture 9 which is similarly shaped, so that the shaft cannot rotate. A plastics bearing sleeve 1 2 surrounds the major portion of the shaft 8 and has an external end flange 1 4 adjacent the inner side of the wall 4. A hollow spool 1 5 of aluminium, for example, is journalled on the shaft 8 by way of the bearing sleeve 1 2 and has a central portion 1 6 with a rectangular off-centre slot having a wider and a narrower portion 18, 19, to permit connection to the spool of an end of a safety belt (not shown).The slot 18, 19, and thus also the belt, is centrally dis posed between the side walls 2, 4. External flanges 20, 21 at the ends of the central portion 1 6 extend outwardly to short sleeve portions of circular cross-section forming coax ial cup-like end portions 22, 24 provided around their entire external peripheries with ratchet teeth 25.

A retractor spring (not shown), for example a spiral spring, is contained within a housing 26 having an annular disc portion with a circular sectioned sleeve portion extending from its outer periphery. The housing 26 is fixedly received in the cup-like end portion 22 of the spool 15, with its disc portion adjacent the side wall 2, mechanically by suitable interfitting formations on the housing and the spool or by an adhesive. The circular hole in the disc portion on the axis of the housing 26 is of such diameter that the housing can rotate with the spool 1 5 without fouling the square sectioned shaft portion 11.The outer end of the spring is attached to the inside of the circular sectioned sleeve portion of the housing 26 by any suitable means, and the inner end is formed into a hollow end portion of square cross section which is non-rotatably located on the square sectioned shaft portion 11. The retractor spring biasses the spool 1 5 to rotate to wind in the belt on the spool portion 1 6.

Initially, the retractor spring is held in the housing 26 in the wound condition by means of an element which engages the spring end and is collapsible or displaceable and is formed with or fitted to the housing. The element is preferably a collapsible plug received in the hollow end portion and in nonrotatable engagement with the housing. Assembly into the retractor is effected by first placing the housing 26 with the spring received therein within the spool end portion 22 and then placing these two components within the frame. The shaft 8 is inserted through the aperture 20 and the spool 1 5. As the shaft end portion 11 enters the spring inner end portion, it compresses the collapsible plug and finally entirely displaces it from the housing 26 as the shaft end portion nonrotatably engages in the aperture 9 in the side wail 2.

The teeth 25 on the spool 1 5 constitute part of a locking mechanism operable to prevent rotation of the spool in the belt unwinding direction and including also a pawl member 32. The pawl member 32 comprises two pawl portion as 34 joined by a connecting portion 38 extending across the frame between them. Each portion 34 has three pawl teeth 35 and the member 32 is on a shaft 36 extending between the side walls 2, 4 from a rest position illustrated, in which the teeth 35 are spaced from the teeth 25, to a locking position in which the teeth 25, 35 engage.

The pawl portion 34 which co-operates with the teeth 25 on the spool end portion 24 has an outwardly projecting pin 39 by which the pawl member is moved between its rest and locking positions.

The locking mechanism incorporates inertial sensing arrangements accommodated on the inner side of the side wall 4 and partly within the spool end portion 24. The spool 1 5 has a bearing sleeve portion 40 projecting outwardly beyond the flange 21 on which is rotatably received a lock cup member 41, of plastics material, comprising a plate portion 42 adjacent the sidewall 4 from which extends a sleeve portion 44 in bearing relationship with the bearing sleeve portion 40. Concentrically surrounding the sleeve portion 44 is an outer sleeve portion 45 provided with internal ratchet teeth 46. Below the spool 15, the plate portion 42 is provided with projecting fingers 48, 49 which define between them a parallel sided open ended slot within which is received the pin 39 of the pawl member 32.The plate portion 42 also includes an integral spring tongue portion 45 which engages a boss 51 formed on the pawl member 34 below the pin 39. The spring tongue portion 50 and the boss 51 co-operate to maintain the lock cup member 41 normally in the illustrated position.

Journalled on the sleeve portion 44 is an inertia disc 52 provided with diametrically opposed recesses 54 at least one of which contains a tooth member 55 of plastics material pivotally received on a pin 56 extending axially outwardly from the flange 21. The tooth member 55 has an integral radially inwardly projecting spring limb 58 of which the free end engages in the recess 54, so that spool rotation is transmitted to the inertia disc 52. The recess 54 has towards its opening adjacent wall portions 59, 60 inclined respectively at greater and lesser angles to the radius intersecting them.

During normal belt protraction, the tooth member 55 is urged by the limb 58 to engage the wall portion 59, so as to be spaced from the internal teeth 46 of the lock cup member 41 as shown. However, if acceleration of the spool 1 5 in the belt unwinding direction exceeds a predetermined amount, the inertia disc 52 will lag on the spool and the tooth member 55 will ride up onto the wall portion 60 against the bias of the limb 58, until such time as it engages one of the teeth 46. The spool rotation will be thereby coupled to the lock up member 41 which will rotate so that the pin 39 is moved inwardly in the slot between fingers 48, 49, so pivoting the pawl member 32 until the teeth 35 engage with the spool teeth 25 and lock the spool against rotation. The spool rotational speed at which this happens is determined by the resilience of the teeth member limb 58.

In an alternative arrangement, an inertia disc 1 52 is provided with opposed parallel sides 154, at least one of which co-operates with a tooth member 1 55 pivoted on a pin 1 56 projecting axially direction from the flange 21. The tooth member 155 is urged to engage the side 1 54 by a spring strip 158, of which a free end engages the outer side of the tooth member, the other end being secured by three pins 1 59 extending axially from the flange 21.

Normally, the tooth member 1 55 and the inertia disc 1 52 maintain the relationship shown in Fig. 5 under the bias of the spring strip 158, in which the toothed member is spaced away from the teeth 46 of the lock cup 41. If however the spool 1 5 accelerates in the belt protraction direction at more than a predetermined rate determined by the spring force of the spring strip 158, the inertia disc 1 52 will lag on the spool and will tilt the tooth member 1 55 so that its toothed portion engages one of the teeth 46, bringing about locking of the retractor as described above.

The retractor can be locked against belt protraction in response also to a predetermined acceleration (or deceleration) of the retractor itself, and thus of a vehicle in which it is secured. To this end, the lower part of the lock cup member 51 mounts a locking lever 62 for pivotation, by a vehicle sensitive inertial device, about an axis parallel to the spool axis from a rest portion shown, in which a toothed end portion 64 of the lever is spaced from the teeth 25 of the spool end portion 24, to a position in which the end portion engages one of those teeth. This engagement drivingly couples together the spool 1 5 and the lock cup member 41, so that spool rotation turns the lock cup member about the spool axis to effect retractor locking as previously described.

The vehicle sensitive inertial device comprises a housing holder 65 of plastics material in the form of two walls at right angles. From one wall, a pin 66 extends perpendicularly outwardly, parallel to the spool axis, for reception in a hole in the lock cup member lower portion, beneath the lever 62. The other wall of the holder 65 has a hole of circular crosssection of which the axis is perpendicular to but in the same plane as that of the pin 66.

The hole serves to receive a pin 68 protruding from a housing 69, also of plastics material, which has an upwardly opening recess with a conical floor 70 on which rests an inertia body 72 in the shape of a ball. The housing 69 also mounts a lever 74 for pivotation about an axis parallel to the spool axis, the lever having a downwardly facing conical recess normally axially aligned with the conical floor 70 by which it rests on the inertia ball 72. The lever 74 has an upper surface 76 which is part spherical and on which the locking lever 62 rests. In the normal position illustrated, this surface 76 is concentric with the ball 42, the centre of which lies in the plane containing the axes of the pins 66 and 68 of the housing holder 65 and the housing 69.

A sufficient acceleration or deceleration of the retractor will cause the inertia ball 72 to ride up the floor 70 of the holder 69 to thereby pivot the lever 74 upwardly and consequently pivot upwardly the locking lever 62 also, so that its toothed portion engages in the spool teeth 25 and locking follows as described above.

The mounting of the housing holder 65 on the lock cup member 41 by means of the pin 66, and the mounting of the housing 69 on the holder by means of the pin 68 permits the orientation of the housing within the retractor to be selectively varied about axes parallel to and perpendicular to that of the spool, and because the axes of the two pins intersect at the centre of the ball 72 this remains in its rest position, provided the axis of the conical floor 70 remains at least approximately vertical. Also, because the part spherical surface 71 of the lever 74 is concentric with the ball 72, the position of the locking lever 62 remains unchanged, provided it can still engage the lever 74 within the area of the part spherical surface.

In use, the housing 69 and holder 65 are positioned so that the axis of the conical floor 70 is vertical, either on assembly of the retractor or during installation in a vehicle. If the positions are preset, the housing and holder can be frictionally secured or cemented in place as an assembly step, but if adjustment is to be possible after assembly, the free ends of the pins 66, 68 can be provided with screwdriver slots to permit adjustment. The housing and holder can being frictionally held in the desired position or detent means can be provided between the holder and the lock cup member and between the housing and the holder to releasably retain the parts in a selected one of a plurality of different positions.

In an alternative arrangement shown in Figs. 7, 8 and 9, the lower end of the lock cup member 41 has a projection providing a loop 165 extending in a plane at right angles to the frame walls 4 and 5, away from the wall 4, within which is received the part spherical undersurface of a housing member 1 69 having recess with a conical surface 1 70 at its upper side in which rests an inertia ball 1 72. Resting on the inertia ball is a locking lever 162 pivoted on the lock cup member 41 and having a tooth at its free end engageable with the ratchet teeth 25 of the spool end portion 24.

The undersurface of the housing member 1 69 is concentric with the inertia ball 1 72 in its rest position shown, so the housing member can be moved relative to the support loop 1 65, within a range dictated by the area of the undersurface, without disturbing the rela tionship of the ball to the locking lever 1 62.

Consequently, the axis of the conical support surface 1 70 can be selectively positioned to be vertical in use over a range of orientations of the retractor. The position of the housing member 1 69 is preferably preset during as sembly and maintained by means of an adhe sive.

In a further alterntive arrangement shown in Fig. 10, the lower end of the lock cup mem ber 41 is provided with an inwardly projecting portion having at its upper side a recess with a part spherical surface 265. Received within this recess is a housing 269 provided on its upper surface with a conical recess 270 in which an inertia ball 272 is received. The lower part of the housing 269 can engage the surface 262 either on a circular line of contact, as shown, or the lower part of the housing can itself be part spherical to make surface-to-surface contact. A locking lever 262 pivoted on the member 41 for movement to engage the spool teeth 25 rests on the top of the inertia ball 272.The part spherical surface 265 is concentric with the inertia ball 272 in its normal position, so that housing 269 can be moved to maintain the axis of the recess 270 vertical within a range dictated by the area of the part spherical surface whilst accommodating various orientations of the retractor. In this arrangement, the orientation of the housing 269 is preferably preset assembly, the housing being thereafter secured in place by adhesive.

In both the arrangements of Figs. 7 to 9 and Fig. 10, the tooth portion of the locking lever 162, 262 is normally spaced from the teeth 25 and the ball 172, 272 is centered in the conical floor 170, 270 but in response to a sufficient retractor acceleration, the ball rides up the conical floor of the recess to pivot the lever to engage its tooth portion with the ratchet teeth 25 and thus effects locking in the manner previously described.

It will be evident that the retractor described can be modified in various ways within the scope of the invention. For example, by omission of appropriate parts, the retractor can be made only belt acceleration sensitive or only retractor acceleration sensitive as shown. Futher features of the modified and unmodified embodiments described can be transferred freely from one embodiment to another.

Claims (41)

1. A vehicle seat belt retractor comprising a spool having an end of a seat belt secured thereto, a frame having spaced-apart portions between which the spool is rotatably supported, a retractor spring biassing the spool to rotate to wind the belt thereon and a locking mechanism arranged to lock the spool against belt protraction in response to a predetermined condition, in which the spool has a lesser cross-section portion on which the belt is wound and a portion of greater cross section which has locking formations thereon and which axially overlaps at least a part of the retractor spring or locking mechanism.

2. A retractor according to claim 1, in which the axially overlapping portion of the spool is a cup-like portion at one end of the spool, the locking formations being on the outer surface of the cup-like portion.

3. A retractor according to claim 2, in which the spool has an axially-overlapping cup-like portion at each of its ends, each cup like portion having locking formations on its surface and the cup-like portions at least partially receiving the retractor spring and the locking mechanism respectively.

4. A retractor according to any preceding claim, in which the locking formations com prise a set of ratchet teeth on at least one greater cross-section portion, the locking mechanism including a locking member having a respctive pawl portion for the or each set of ratchet teeth.

5. A retractor according to claim 4, in which the or each pawl portion has a plurality of locking teeth which are arranged for simultaneous engagement with respective ones of a plurality of ratchet teeth of the or each set of teeth.

6. A retractor according to claim 4 or 5, in which the locking member is rotatably supported by the spaced-apart frame portions and is pivotable about an axis extending paral lel to the spool axis between first and second positions in which the or each pawl portion is respectively spaced from and engaged with its corresponding set of ratchet teeth.

7. A retractor according to any one of claims 4 to 6, in which the locking mechanism includes a rotatably-mounted inertia member which is housed in an axially-overlapping portion of the spool, the inertia member being arranged to rotate with the spool at spool accelerations below a predetermined threshold value and to lag relative thereto at accelerations equal to or exceeding the threshold value, an operating member which is operatively connected to the locking member and which has a cylindrical portion which extends around the inertia member and is at least partially housed in the said axially-overlapping, spool portion, and means for coupling the inertia member and the cylindrical operating member portion for joint rotation of the inertia and the operating members when the inertia member lags relative to the spool, the operating member upon such rotation causing movement of the locking member from its first to its second position.

8. A retractor according to claim 7, in which the coupling means comprise a pawl member pivotally mounted adjacent the inertia member and ratchet teeth on the cylindrical operating member portion engageable with the pawl member to effect coupling, the pawl member having an integral resilient portion which is in engagement with the inertia member and deforms resiliently when the pawl member pivots to engage the ratchet teeth.

9. A retractor according to claim 8, in which the pawl member is located in a recessed portion of the periphery of the inertia member and engages a surface of the inertia member to be cammed outwardly into engagement with the operating member ratchet teeth when the inertia member lags relative to the spool.

10. A retractor according to claim 7, in which the coupling means comprise a pawl member pivotally mounted adjacent the inertia member and ratchet teeth on the cylindrical operating member portion engageable with the pawl member to effect coupling, the pawl member being biassed by a resilient means into sliding contact with the periphery of the inertia member and the point of contact moving outwardly from the spool axis when the inertia member lags relative to the spool.

11. A retractor according to claim 10, in which the pawl member is in sliding contact with a straight side portion of the inertia member.

1 2. A retractor according to claim 11, in which the inertia member has a further straight side portion extending parallel to the said portion and equidistantly-spaced from the axis of rotation of the inertia member.

1 3. A retractor according to any one of claims 10 to 12, in which the resilient means comprises a leaf spring secured at one of its ends to the spool and in sliding contact with the pawl member at its other end.

14. A retractor according to any preceding claim, including an inertial retractor acceleration sensing device which has a member engageable with the locking formations of the spool.

1 5. A retractor according to any preceding claims, in which an axially-overlapping portion of the spool overlaps the retractor spring which is housed in the overlapping portion by a closure member having an end wall which extends transversely to the spool axis to close an open end of the overlapping portion.

1 6. A retractor according to claim 15, in which the closure member has an axially extending peripheral portion which engages an inner surface of the overlapping portion.

1 7. A retractor according to any preceding claim, in which the spool has an axial bore and is rotatably supported on a shaft extending between the spaced apart portions of the frame.

1 8. A vehicle seat belt retractor comprising a spool having an end of a seat belt secured thereto, a frame having spaced-apart portions between which the spool is rotatably supported, a retractor spring biassing the spool to rotate to wind the belt thereon and a locking mechanism arranged to lock the spool against belt protraction in response to a predetermined condition, in which the spool has a bore and rotates on a shaft passing through the bore and extending between the spacedapart portions of the frame.

1 9. A retractor according to claim 1 7 or 18, in which the shaft has an end portion shaped to cooperate with an apeture in one of the spaced-apart portions in order to prevent rotation of the shaft relative thereto.

20. A retractor according to any one of claims 1 7 to 19, in which a bearing sleeve of plastics material is positioned between the shaft and the wall of the bore in the spool.

21. A retractor according to any one of claims 1 7 to 20, in which the spool has a slot extending therethrough and spaced from the bore, an end of the seat belt being secured in the slot.

22. A method of assembling a vehicle seat retractor comprising a spool having an end of a seat belt secured thereto, a frame having spaced-apart portions between which the spool is rotatably supported, a retractor spring biassing the spool to rotate to wind the belt thereon and a locking mechanism arranged to lock the spool against belt protraction in response to a predetermined condition, the method comprising the steps of connecting the outer end of the retractor spring to the spool at a position radially spaced from the spool axis, the spring being in a wound condition, inserting a shaft into an axial bore of the spool and into engagement with the inner end of the spring and locating an end portion of the shaft non-rotatably in an aperture in a spaced portion of the frame to secure the inner end of the spring against movement relative to the frame.

23. A method accordng to claim 22, in which the shaft is inserted into the spool bore after alignment of the bore with respective apertures in the spaced portions of the frame.

24. A method according to claim 22 or 23, in which the shaft has a cup-like end portions and, before fitting to the spool, the spring is held in its wound condition in a housing receivable in the cup-like end portion, the spring and housing then being inserted into the end portion prior to insertion of the shaft into the spool bore and the inner end of the spring being located in the housing in a position in which it is engaged by the shaft.

25. A method according to claim 24, in which the inner end of the spring is located in the housing by a portion of the housing which is displaced by the shaft upon its insertion.

26. A vehicle seat belt retractor comprising a spool having an end of a seat belt secured thereto, a frame having spaced-apart portions between which the spool is rotatably supported, a retractor spring biassing the spool to rotate to wind the belt thereon and a locking mechanism arranged to lock the spool against belt protraction in response to a predetermined condition, the retractor including an inertial retractor acceleration sensing device laterally spaced from the spool, the device comprising a support for an inertial body permitting displacement of the body from a rest position in response to a predetermined retractor acceleration, a locking lever pivotable to lock the retractor against belt protraction in response to such displacement, and means mounting the support for selective rotation about at least one axis extending substantially through the centre of gravity of the body to maintain the body normally in its rest position over a range of orientations of the retractor without substantial change in the operative relationship between the body and the locking lever.

27. A retractor according to claim 26, in which the mounting means mount the support for selective rotation about two mutually-perpendicular axes each extending substantially through the centre of gravity of the body.

28. A retractor according to claim 26 or 27, in which the inertial body is spherical.

29. A retractor according to any one of claims 26 to 28, in which the inertial body is supported on a conical sealing of the support.

30. A retractor according to any one of claims 26 to 29, in which the support pivotally mounts an operating lever having an output surface engaging the locking lever, the output surface being substantially centred on the centre of gravity of the body.

31. A retractor according to claim 30, in which the oprrating lever has a conical surface in contact with the inertial body.

32. A retractor according to any one of claims 26 to 29, in which the locking lever is in direct contact with the inertial body.

33. A retractor according to any one of claims 26 to 32, in which the mounting means for the support comprises a mounting member on which the support is mounted and relative to which the support is movable about two mutually-perpendicular axes, the mounting means including a part-spherical surface on at least one of the mounting members and the support, the or each part-spherical surface being substantially centred on the centre of gravity of the inertial body.

34. A retractor according to claim 33, in which the support has a part-spherical lower surface and the mounting member comprises a loop in which the support is supported.

35. A retractor according to claim 33, in which the mounting member has a part-spher ical surface with which the support is in contact on a circular line of contact.

36. A retractor according to claim 33, in which the mounting member and the support have mutually-contacting part-spherical surfaces.

37. A vehicle seat belt retractor comprising a spool having an end of a seat belt secured thereto, a frame having spaced-apart portions between which the spool is rotatably supported, a retractor spring biassing the spool to rotate to wind the belt thereon and a locking mechanism arranged to lock the spool against belt protraction in response to a predetermined condition, in which the locking mechanism includes a rotatably-mounted inertia member which is arranged to rotate with the spool at spool accelerations below a predetermined threshold value and to lag relative thereto at accelerations equal to or exceeding the threshold value, an operating member and means for coupling the inertia member and the operating member for joint rotation to effect locking of the retractor, the coupling means comprising a coupling member pivotally mounted on the spool adjacent the inertia member and having an integral resilient portion which is in engagement with the inertia member and pivots outwardly to engage the operating member when the threshold value is achieved, the integral resilient portion deforming resiliently during such pivoting movement.

38. A vehicle seat belt retractor comprising a spool having an end of a seat belt secured thereto, a frame having spaced-apart portions between which the spool is rotatably supported, a retractor spring biassing the spool to rotate to wind the belt thereon and a locking mechanism arranged to lock the spool against belt protraction in response to a predetermined condition, in which the locking mechanism includes a rotatably-mounted inertia member which is arranged to rotate with the spool at spool accelerations below a predetermined threshold value and to lag relative thereto at accelerations equal to or exceeding the threshold value, an operating member and means for coupling the inertia member and the operating member for joint rotation to effect locking of the retractor, the coupling means comprising a coupling member pivotally mounted on the spool adjacent the inertia member and is in sliding contact with a straight side portion of the inertia member.

39. A vehicle seat belt retractor substantially as hereinbefore described with reference to Figs. 1 to 4 or Figs. 1 to 4 modified in accordance with Figs. 5 and 6 of the drawings.

40. A vehicle seat belt retractor according to claim 39 and modified substantially as hereinbefore described with reference to Figs.

7 to 9 or Fig. 10 of the drawings.

41. A method of assembling a vehicle seat belt retractor, the method being substantially as hereinbefore described.