GB2282055A - A seat belt pretensioner - Google Patents

Abstract

A pyrotechnic pretensioner arrangement of an emergency locking seat belt retractor or associated with a buckle anchorage, has a gas pressure activated piston (2) and a spring biased gas generator (8) in a generally parallel cylindrical bores (3, 7) provided in an assembly (4) which, in an emergency is inertially movable about a pivot (5) against a calibration spring (15) to release a catch formed by a lever arm (9). Release of the catch enables the force of a spring (18) to drive the gas generator (8) downwards against a firing pin (10) whereafter, the gases pass through passage (17) to move piston (2) upwards and thereby apply tension via a cable (1). <IMAGE>

Description

SAFETY RESTRAINT PRETENSIONING APPARATUS This invention relates to safety restraint pretensioning apparatus and relates especially to pretensioning of the webbing of a seat belt by rotation of an emergency locking webbing retractor reel.

A typical vehicle seat belt comprises a length of webbing one end of which is anchored to the vehicle near the floor at one side of the seat so that the webbing can pass therefrom across the lap of an occupant, through a buckled buckling tongue and diagonally upwards across the occupant to a shoulder height guide via which it is wound onto a reel of a suitably positioned emergency locking retractor. In the case of a car front seat restraint such retractor may be positioned within the respective 'B'-post. For user comfort, such retractors have low-friction bearings and only a light rewind spring. In order to eliminate undue payout of webbing from the reel after lock up of the reel in an emergency, it has been proposed to provide pretensioning means which is able to sense the early stages of a crash and apply a rapid rotation of the retractor reel to tighten the webbing against the occupant. Such a pretensioning means may comprise a gas generator or pyrotechnic device which applies gas pressure to a piston which is coupled to the reel by a suitable cable and pulley mechanism to rotate the reel up to a predetermined amount. One such pretensioning mechanism has been described in the Specification of European Patent Application No. 0 529 501. In the latter, a gas generator forms a part of an assembly mounted on an emergency locking webbing retractor and the assembly is able to move against the action of a calibration spring to release a catch mechanism. The release of the catch mechanism enables the gas generator to move under the influence of a spring and self-detonation occurs by striking a firing pin or the like.

The object of the present invention is to provide an improved mechanism permitting the conditions for firing the gas generator to be more precisely predetermined.

According to the present invention there is provided a safety restraint pretensioning mechanism comprising supporting means and an assembly supported thereby to be movable away from a normal rest position, said assembly including pretensioner means, a catch and a pretensioner activation means movable within said assembly under the influence of a spring as a result of release of the catch characterised in that said catch comprises a lever having a first arm which maintains the activation means in an inactive position and having a second lever arm having a lever surface which normally slideably engages a stop surface carried by the supporting means, at least one of said lever surface and said stop surface extending in a direction approximately corresponding to the direction thereat of movement of the assembly relative to the supporting means whereby in operation relative movement between said lever surface and said stop surface enables the second lever arm to move out of engagement with the stop surface when subjected to a predetermined rate of change of vehicle speed to release the activation means.

In order that the invention may be more clearly understood and readily carried into effect the same will be further described by way of an example with reference to the accompanying drawing in which: Fig. 1, illustrates in fragmented part-sectional diagrammatic form a safety restraint pretensioning mechanism and Fig. 2, illustrates an upward view of a lever catch used in the mechanism of Fig. 1.

Fig. 3, illustrates an upward view of an alternative embodiment of a lever catch.

Referring to Figs. 1 and 2, the mechanism is intended as an extension 6 of the housing of a seat-belt webbing retractor of the emergency locking type, to operate in an emergency via a suitable clutching mechanism. The mechanism is constructed similarly to that described in the aforementioned European Patent Specification. Pretensioning force is transmitted via a cable 1 to a pulley which can rotate the webbing reel of the retractor in a sense to tighten the webbing around the occupant. A typical clutch mechanism has also been described in the Published European Patent Specification No. 0 600 689 and will not be further described herein except to observe that the clutch mechanism is such as to normally permit free and unhampered rotation of the retractor reel but upon actuation of the pretensioning mechanism there is a sharp pull on cable 1 which activates the clutch and provides mechanical connection between cable 1 and the reel.

The cable 1 is connected to a piston 2 which is sealingly axially movable in an elongate cylinder bore 3 formed in an inner movable member 4. The member 4 is pivotally movably supported in the housing extension 6 about a pivot 5 and is inertially movable from a fixed rest position shown against the action of a captive calibration spring 15. The inner member 4 has a further enclosed cylindrical bore 7 within which a cylindrical gas generator 8 is closely slideable and acting generally parallel to the cylinder bore 3. The cylinder 7 communicates with the underside of piston 2 via a passage 17. The gas generator 8 is normally held in an upward position in the bore 7 against the action of a further compressed spring 18, by a pivoted lever arm 9 which projects into and blocks its downward path towards a firing pin 10 carried in a closure 11 of the lower end of bore 7.

A low friction pivot 12 of a catch having a first relatively short lever arm 9 is located in and moves with the member 4 and the catch has a second relatively long bifurcate lever arm 13 as seen in Fig. 2 which passes either side of the path of travel of the gas generator 8, the outer ends of the arm 13 have surfaces 16a which normally rest on surfaces 14a of stops 14 fixedly carried in the housing 6. The stop surfaces 14a extend generally at right angles to the line, in this case the cylinder axis, passing through the pivot axis of 5. The extent of the stop surfaces of 14 is such that movement of the member 4 a predetermined distance in a rightward direction (as seen in the drawing) against the calibration spring 15 causes outward projections 16 of the lever arms 13 which carry surfaces 16a to slide along the stops 14 sufficiently for them to pass downwards over stops 14 to release catch 9. This occurs at more than a predetermined sustained rate of change of vehicle speed.

Such release of catch 9 allows the gas generator 8 to be driven against firing pin 10 by spring 9. The generator is thereby detonated and gas emanates from apertures (not shown) in the upper end thereof so that a resulting rapid gas pressure elevation is communicated from cylinder 7 via a passage 18 to the underside of piston 2. This causes upward movement of piston 2 and applies tension to cable 1 to pretension the retractor reel (not shown).

Following completion of the upward movement of piston 2 and cable 1, the subsequent tension applied to the belt webbing by the occupant is sustained by the emergency locking components of the retractor itself and the cable 1 does not need to support crash loads exerted by the safety restraint webbing.

In the assembly of Fig. 1, the inertial mass of housing 4 and its contents and the spring 15 are so selected and the assembly is mounted on the seat-belt retractor with such orientation in relation to the normal forward direction of vehicle movement that a said predetermined sustained forward deceleration will release the catch 9.

In a modification of the arrangement shown in Fig. 1 and in Fig. 2 wherein the lever 13 has two arms engaging with respective stops 14, one such arm may be omitted as shown in Fig. 3. This will avoid a statistical possibility that having regard for manufacturing tolerances one arm could disengage from its stop slightly in advance of the other. Such action could possibly result in inadvertent catching of the mechanism and spurious operation.

In either case, the force which resists the movement of the assembly about the pivot 5, introduced by the friction at stops 14 is proportional to the force exerted at 9 but the mechanical advantage of the lever acting about pivot 12 diminishes such frictional force to an almost insignificant value having regard to the deceleration calibration of the device by the spring 15.

Whilst in the mechanism described in the foregoing, the first relatively short lever arm 9 is designed to itself directly engage and block the movement of the gas generator the lever arm 9 may if desired be designed to cooperate with a detent which provides the blocking engagement. The lever arm 9 may then be designed for example to act in the manner of a cam.

By virtue of the design of the sensing mechanism described in the foregoing, the lever arm or arms 13 can be of such length and the forces of spring 9 and 15 can be of such values that values of vehicle rate of change of speed which are less than a predetermined value at which firing is required can result in sliding movement of lever ends 16 along stops 14 and subsequent return to the normal rest position. A sensitive and quite precise calibration setting of the pretensioning apparatus is therefore attainable.

Whilst the present invention has been more particularly described with reference to a pretensioner for combining with a seat belt webbing retractor, a pretensioner according to the invention may be adapted to tighten a seat belt, for example by shortening a buckle anchorage.

Claims (7)

1. A safety restraint pretensioning mechanism comprising supporting means and an assembly supported thereby to be movable away from a normal rest position, said assembly including pretensioner means, a catch and a pretensioner activation means movable within said assembly under the influence of a spring as a result of release of the catch wherein said catch comprises a lever having a first arm which maintains the activation means in an inactive position and having a second lever arm having a lever surface which normally slideably engages a stop surface carried by the supporting means, at least one of said lever surface and said stop surface extending in a direction approximately corresponding to the direction thereat of movement of the assembly relative to the supporting means whereby in operation relative movement between said lever surface and said stop surface enables the second lever arm to move out of engagement with the stop surface when subjected to a predetermined rate of change of vehicle speed to release the activation means.

2. A safety restraint pretensioning mechanism as claimed in claim 1, wherein said first arm normally projects into the path of movement of the activation means and is movable pivotally out of said path when permitted by movement of the second lever arm surface out of said engagement with the stop surface.

3. A safety restraint pretensioning mechanism as claimed in claim 1 or 2, wherein said second lever arm extends outside the path of movement of the activation means.

4. A safety restraint pretensioning mechanism as claimed in claim 1, 2, or 3 wherein said second lever arm has two portions extending around either side of the path of the activation means.

5. A safety restraint pretensioning mechanism as claimed in claim 3 or 4 wherein said pretensioner means and said activation means act in generally parallel paths and said lever arm or said portion thereof extend also outside the path of a connection between the pretensioning means and a retractor reel.

6. A safety restraint pretensioning mechanism as claimed in claim 1, 2 or 3, wherein said assembly is biased into said normal rest position by a captive calibration spring.

7. A safety restraint pretensioning mechanism as claimed in any of claims 1 to 6 wherein said activation means comprises a pyrotechnic gas generator adapted to be detonated by an impact under the influence of said spring.