VEHICLE SEAT BELT RETRACTOR

Abstract: The web-locker retractor has a pair of identical clamping wedges 10 having teeth which are shaped to penetrate the material of a seat belt in order to displace the fibres of the material and engage therewith. Upon an engagement with the belt, the teeth interfit with those of one wedge fitting between those of the other. The teeth are arranged in arrays 12, 14 one of which is an offset mirror image of the other. The teeth of the two arrays are inclined oppositely to the direction of belt protraction. Posts 22, 26, 32 and sockets 20, 24, 30 on the wedges co-operate to restrain the wedges to move perpendicularly to the belt plane, against a biassing spring (not shown). Upon locking, the web locker does not deflect the belt and therefore does not have to overcome a component of the tensile load on the belt. A retractor of light construction is therefore possible.

Description: This invention relates to vehicle seat belt retractors of the type which include a belt storage device, usually a spool, and a clamping device which engages the belt to prevent protraction thereof from the storage device. Such a clamping device is often called a "web locker". Examples of vehicle seat belt retractors which include web lockers can be found in patent specifications GB-A-2 113 978, GB-A-2 126 876 and GB-A-2 177 891. In all these specifications, the retractor has a belt storage spool and a web locker which comprises one or a pair of clamping wedges. The or each wedge has a planar front face for engagement with the belt and extending parallel to the plane thereof. A rear face of the or each wedge, inclined to the front face, is in sliding contact with an oppositely-inclined surface on the retractor frame. The wedge or wedges are moved towards the belt, and into clamping engagement therewith, when they are acted upon by an operating means of the retractor which produces a force directed substantially in the direction of protraction of the belt. The movement of the wedge(s) into engagement with the belt has a substantial component in the direction of belt protraction. A web locker retractor of a different type is described in patent specification EP-A-0 185 367. Here a clamping block mounted on a swinging arm is brought into clamping engagement with the belt in order to arrest protraction of the belt from a storage spool. The surface of the block which contacts on face of the belt has a close-packed array of teeth, whilst a surface of the retractor frame with which the other face of the belt is pushed into contact has a low coefficient of friction and is, for example, a surface of a layer of polytetrafluoroethylene. In contrast to the retractors discussed above, the clamping block moves to its clamping position substantially perpendicularly to the plane of the belt; this movement has no significant component in the direction of belt protraction. Patent specifications DE-A-3 306 434 (corresponding to the preamble of claim 1) and US-A-3 504 867 describe safety belt systems in which web-lockers having corrugated jaws are operable to divert a run of seat belt from a linear path into a zig-zag path, in which protraction of the belt is prevented by a capstan-like action of the jaws on the belt. In these web-lockers, a component of the tensile load on the belt acts against the web-locker clamping force and therefore tends to resist clamping. This increases the response time of the web-locker and requires the web-locker to be mounted in a structure which is very strong and rigid and correspondingly heavy. The present invention is concerned with the provision of a more efficient web-locking retractor, particularly one which can meet the increasingly more stringent standards which authorities are continually laying down. These standards include ones directed to the rapidity and security of locking of seat belt retractors and set criteria which have to be met even when the seat belt surface is contaminated by substances such as oil, mud and the rust-proofing compounds which are often applied to motor vehicles. Such criteria are obviously important in retractors which include web lockers because locking relies, at least in part, on engagement of the web locker with the seat belt. Rapidity of locking is of course desirable so that the least amount of belt protraction, and hence forward movement of the seat belt user, takes place before protraction is arrested. Because some motor manufacturers specify very stringent maximum weight requirements, it is also desirable for a web-locker retractor to be relatively light in weight, whilst still being able to resist a specified tensile load on the seat belt. According to the present invention, there is provided a vehicle seat belt system comprising a belt, clamping means for the belt and operating means for the clamping means, the operating means being responsive to a threshold acceleration to cause operation of the clamping means which comprises first and second belt-engagement surfaces which are relatively movable towards each other and into engagement with the belt so that protraction of the belt is prevented, the belt-engagement surfaces having protruding formations arranged so that, upon engagement with the belt, the formations of the surfaces interengage with the belt therebetween, the belt-engagement surfaces being surfaces of respective first and second clamping members which, upon operation, move towards each other and into engagement with the belt, characterised in that, upon operation, the belt is substantially undeflected between the clamping members, the protruding formations being shaped to penetrate into the material of the belt in order to engage therewith in the clamping position of the clamping means and comprising respective arrays of teeth each consisting of a plurality of rows of teeth extending transversely of the belt, the rows of each array being spaced apart to define inter-row spaces and the rows of one array being aligned across the belt with the inter-row spaces of the other array. Such a web locker arrangement can be incorporated into a seat belt retractor having belt storage means (which will usually comprise a storage spool) or can be located elsewhere in the seat belt system. As used herein, the term "threshold acceleration" also comprehends deceleration of the belt and/or a vehicle in which the belt system is mounted. With a system according to the invention, a particularly positive and secure clamping of the belt can be achieved and, accordingly, belt protraction after onset of the threshold acceleration can be reduced to a low value. Relevant safety requirements can be met, particularly those requirements which call for effective clamping of a contaminated belt. Moreover, since the belt-engagement surfaces move towards each other to engage the belt and because the clamping surface formations penetrate the material of the belt to engage therewith, the belt is substantially undeflected from its operating plane during clamping. Accordingly, clamping is effected without movement of the belt-engagement surfaces towards the belt being resisted by the tensile load on the belt. As a result, the retractor can be of lighter construction than would be the case if it had to withstand such forces being transferred to the clamping means. Conveniently, the belt-engagement surfaces are front surfaces of respective clamping wedges, for example wedges of the type shown in specifications GB-A-2 126 876 and GB-A-2 177 891. It is accordingly a preferred feature of the present invention that the first and second belt-engagement surfaces are front surfaces of respective clamping wedges which each have a rear surface which is inclined to the belt protraction direction and is in sliding contact with an oppositely-inclined surface of a further member, whereby, upon relative sliding movement between the wedges and the further members in response to the operating means, the belt-engagement surfaces move into engagement with the belt. More preferably, the further members are fixed parts of the retractor frame and the wedges are moveable relative thereto in response to the operating means. When the or each belt-engagement surface is movable into engagement with the belt with a movement having a component in the belt-protraction direction, initial contact with the protracting belt will tend to cause the engagement surface to be drawn by the belt in the protraction direction and thus into clamping engagement with the belt. Particularly rapid clamping can thus be obtained. In a preferred arrangement, each array of teeth is divided into two zones about a line, preferably extending in the belt-protraction direction, the zone to one side of the line being an offset mirror image of the other zone. Such a construction can make it possible for the belt-engagement surfaces to be surfaces of identical elements which, when positioned to face each other on opposite sides of the belt, will interact in accordance with the invention. Economies in manufacture can thus be achieved. It is preferred that the formations of the belt-engagement surfaces engage the belt to produce a clamping force which has components in the plane of the belt and respectively parallel to the belt-protraction direction and perpendicular thereto. Such an arrangement assists in making the belt-engagement surfaces effective with a range of types of belt webbing. To achieve such force components, the formations may comprise teeth which are inclined to the belt-protraction direction, at, for example an angle of about 20 degrees thereto. Advantageously the teeth are in two zones lying to opposite sides of a line, preferably extending in the belt-protraction direction, the teeth of the two zones being oppositely-inclined relative to the line. Conveniently, each tooth is symmetrical about a median line which is inclined to the belt-protraction direction. Preferably, the leading edge or face of each tooth relative to the direction of belt protraction is slightly undercut and makes an angle of, for example, about 5 degrees with a line normal to the plane of the belt. The trailing edge or face of each tooth is preferably inclined at an angle of 20 to 40 degrees to the plane of the belt. Most preferably, the teeth have irregular pyramidal shapes, the vertex of the pyramid being somewhat rounded and the pyramid having a leading undercut face, inclined at about 5 degrees to the normal to the plane of the belt, a trailing face inclined at 30 degrees to the belt plane and side faces making angles of 65 to 70 degrees with the plane of the belt. The irregular shape of the teeth again assists in making the belt-engagement surfaces effective with a range of webbing types. Preferably, the belt-engagement surfaces are surfaces of clamping members which have means restraining the members for movement relative to each other in directions perpendicular to the belt plane. These restraining means conveniently comprise one or more posts protruding from each member and received in corresponding apertures in the other member. In such constructions, it is again possible to employ two identical clamping members, the restraining means of which interengage when the members face each other across the belt of the retractors. Manufacturing economics can thus again be achieved. Advantageously, resilient biassing means act between the clamping members to bias these apart. The biassing means conveniently comprise a compression spring around any said post provided. An embodiment of the invention will now be described with reference to the drawings of this specification. In the drawings: Figure 1 is a plan view of the clamping surface of a clamping wedge of a web locker of a vehicle seat belt retractor, Figure 2 is a sectional view on the line II-II of Figure 1, Figure 3 is a sectional view on the line III-III of Figure 1, Figure 4 is a plan view of one tooth of the clamping wedge of Figure 1, Figure 5 is a side view of the tooth of Figure 4, and Figure 6 is an end view of the tooth of Figure 4 showing the leading face of the tooth. The clamping wedge shown in the drawings may be used in a vehicle seat belt retractor similar to those shown in patent specifications GB-A-2 126 876 and GB-A-2 177 891, the contents of which are incorporated into this specification by reference, in replacement for the clamping wedges of the retractors described in those specifications. For information about the construction of the retractors, reference should now be made to the two specifications referred to. The wedge shown in the drawings is moulded from a thermosetting resin material such as Vynckier "Vyncolite" Thermoset RX613. Any other material of sufficient rigidity could alternatively be used. The clamping surface of the wedge is visible in Figure 1. It will be seen that the wedge has a base surface 10 from which respective first and second arrays 12, 14 of teeth protrude, the arrays lying respectively to the left and right (as shown in Figure 1) of a centre line 16 which extends longitudinally of the seat belt. The teeth of the second array 14 are a mirror image about a plane extending perpendicularly to the plane of the paper and including the centre line 16 of the teeth of the first array 12, except that the teeth of the second array 14 are staggered in both the x- and y- directions (i.e. perpendicularly and parallel to the line 16 respectively) relative to the teeth of the first array 12. The teeth of each array are arranged in rows extending perpendicularly to the centre line 12. The teeth of each row are spaced with a pitch (hereinafter "x-pitch") of approximately 1.50 mm. The rows of teeth in each array are spaced with a pitch (hereinafter "y-pitch") of 3.40 mm. The extent of each tooth in the x-direction is approximately 0.80 mm, whilst each tooth has an extent in the y-direction of approximately 1.50 mm. The staggering of the second array 14 relative to the first array 12 is such that each tooth of the second array is displaced from its mirror-image position in both the x-direction and the y-direction by distances equal respectively to one-half of the x-pitch and one-half of the y-pitch. Adjacent the left-hand side edge of the wedge (as seen in Figure 1), the wedge is moulded to have, in succession from the end of the wedge which is lowermost in Figure 1, a cylindrical recess 20, a first cylindrical post 22 and a first U-shaped cut-out 24. The axes of the recess 20 and the post 22 extend perpendicularly to the base surface. Adjacent the right-hand side edge of the wedge there are, again in succession from the lower end edge, a second cylindrical post 26, which extends perpendicularly to the base surface and is surrounded by an annular recess 28, a second U-shaped cut-out 30 extending to the right-hand side edge of the wedge and a third cylindrical post 32. The second and third cylindrical posts 26, 32 extend perpendicularly to the base surface and are dimensioned for reception in the cylindrical recess 20 and the first U-shaped cut-out 24 of an identical clamping wedge. Similarly, the first cylindrical post 22 is dimensioned for reception in the second U-shaped cut-out 30 of an identical wedge. The rear face 34 of the clamping wedge is visible in Figures 2 and 3. It is inclined at an angle of about 10 degrees to the clamping surface and is thus positioned for sliding contact with wedged surfaces of an appropriately shaped cavity of a seat belt retractor such as that shown in GB-A-2 113 978 or GB-A-2 177 891. The rear face of the clamping wedge has a layer 36 of low-friction material, for example polytetrafluoroethylene. Alternatively or additionally, low-friction material could be applied to the surfaces of the retractor cavity contacted by the clamping wedges. When two clamping wedges as shown in Figure 1 are assembled in a web-locking retractor, the co-operation between the two wedges is similar to that suggested by the combination of Figures 2 and 3. In such co-operation, the first cylindrical post 22 of each wedge is received in the second U-shaped cut-out 30 of the other wedge, each second cylindrical post 26 is received in the cylindrical recess 20 of the other wedge and each third cylindrical post 32 is received in the first U-shaped cut-out 24 of the other wedge. Further, each post 26 is surrounded by a helical compression spring (not shown in the drawing) which is seated at its ends on the ends of the recesses 20, 28 of the two wedges which are thus constrained to move relative to each other against the bias of the springs in directions perpendicular to their base surfaces. In the assembled retractor, the belt extends between the clamping surfaces of the wedges, the clamping surfaces being held from contact with the belt by the compression springs. Because of the staggered relationship between the teeth of the first and second arrays 12, 14, the teeth of each first array 12 of one wedge are aligned with spaces between the teeth of the second array 14 of the other wedge and the teeth of the second arrays 14 are aligned with inter-tooth spaces of the first arrays. Thus, when the wedges move towards each other in the direction in which they are constrained, the teeth of the two wedges interfit as their teeth penetrate the webbing to engage therewith to clamp the belt between the clamping faces. Figures 4, 5 and 6 show a clamping wedge tooth in detail. It will be seen that the tooth has a distorted pyramidal shape having four approximately-triangular sides and a base which approximates to a parallelogram. The leading face of the tooth is formed by a slightly undercut face 40 which makes an angle a of 85 degrees with the base surface of the clamping wedge. The trailing face of the tooth is formed by a further face 42 which is inclined at an angle b of 30 degrees to the base surface. Each side face of the tooth is formed by another face 44 or 46 which an angle c of 68 degrees to the base surface. Each tooth has a longitudinal medial line 48 which lies at an angle d of 20 degrees to the longitudinal centre line 16 of the wedge (see Fig.1). In the assembled seat belt retractor, two wedges are fitted together as described above and are received between fixed inclined surfaces with which the rear faces 34 of the wedges are in sliding contact. The fixed surfaces taper inwardly towards each other in the direction of belt protraction. The seat belt lies between the clamping faces of the wedges, the centre lines 16 of which are aligned with the direction of belt protraction. In the free condition of the web locker, the clamping faces are each spaced from the belt which is freely protractable and retractable therebetween. The retractor is arranged to lock upon onset of an acceleration above a threshold value. In such circumstances, operating means of the retractor cause movement of the wedges in the direction of belt protraction. Because of the co-operation between the rear faces 34 of the wedges and the inclined retractor surfaces, the wedges also move together so that their teeth contact the belt. It should be noted that wedge movement thus has a component in the belt-protraction direction. If, as will usually be the case, the belt is undergoing protraction at the time of this movement of the wedges, the initial engagement between the teeth and the belt will cause the wedges to be drawn with the belt in the direction of its protraction. This movement will be additional to any movement imparted to the wedges by the retractor operating means and will enhance the clamping effect of the wedges on the belt. As described above, this clamping is effected with the teeth of one wedge fitting between the spaces between the teeth of the other wedge to clamp the belt therebetween, the teeth of the respective wedges displacing the fibres of the belt as they penetrate the material thereof in order to engage therewith. During this engagement, the component of wedge movement in the protraction direction minimises or avoids relative movement between the belt surfaces and the wedges in the belt-protraction direction at the onset of clamping and is important in producing a clamping engagement which does not subject the belt to significant shear loads which can cause damage to the belt.

Claims: A vehicle seat belt system comprising a belt, clamping means for the belt and operating means for the clamping means, the operating means being responsive to a threshold acceleration to cause operation of the clamping means which comprises first and second belt-engagement surfaces (10) which are relatively movable towards each other and into engagement with the belt so that protraction of the belt is prevented, the belt-engagement surfaces having protruding formations (12, 14) arranged so that, upon engagement with the belt, the formations of the surfaces interengage with the belt therebetween, the belt-engagement surfaces (10) being surfaces of respective first and second clamping members which, upon operation, move towards each other and into engagement with the belt, characterised in that, upon operation, the belt is substantially undeflected between the clamping members, the protruding formations (12, 14) being shaped to penetrate into the material of the belt in order to engage therewith in the clamping position of the clamping means and comprising respective arrays of teeth each consisting of a plurality of rows of teeth extending transversely of the belt, the rows of each array being spaced apart to define inter-row spaces and the rows of one array being aligned across the belt with the inter-row spaces of the other array. A seat belt system according to claim 1, in which the clamping members have means (20, 22, 24, 26, 28, 30, 32) restraining the members for movement relative to each other in directions perpendicular to the belt plane. A seat belt system according to claim 2, in which the restraining means comprise one or more posts (22, 26, 32) protruding from each member and received in corresponding apertures (20, 24, 30) in the other member. A seat belt system according to claim 2 or 3, in which resilient biassing means act between the clamping members to bias the members apart. A seat belt system according to any preceding claim, in which the movement of each clamping surface has components parallel and perpendicular to the belt-protraction direction. A seat belt system according to claim 5, in which the first and second belt-engagement surfaces are front surfaces of respective clamping wedges. A seat belt system according to any preceding claim, in which the formations of the belt-engagement surfaces engage the belt to produce a clamping force which has components in the plane of the belt and respectively parallel to the belt-protraction direction and perpendicular thereto. A seat belt system according to any preceding claim, in which each array of teeth is divided into two zones by an imaginary line (16), the zone to one side of the line being an offset mirror image of the other zone. A seat belt system according to claim 8, in which the line (16) extends in the belt-protraction direction. A seat belt system according to any preceding claim, in which the teeth (12, 14) are inclined to the belt-protraction direction. A seat belt system according to claim 10, in which the teeth are inclined at about 20° to the belt-protraction direction. A seat belt system according to any preceding claim, in which the leading face (40) of each tooth relative to the direction of belt-protraction is undercut. A seat belt system according to claim 12, in which the leading face of each tooth makes an angle of about 5° with a line normal to the plane of the belt. A seat belt system according to any preceding claim, in which the clamping means and the operating means are incorporated into a seat belt retractor which has belt storage means for the seat belt.

Inventors: SMITHSON, ALAN GEORGE
Applicants: BSRD LIMITED
Application year: 1988
Main classification: B60R22
IPC codes: B60R22