PRETENSIONER FOR SEAT BELT RETRACTOR

Abstract: A pretensioner (12) for a vehicle safety restraint belt retractor comprises a linearly displaceable member such as a piston (2) driven by a gas generator (7) in the event of a crash to move tangentially against a rotatable part (1) coupled to the retractor reel to rotate the reel in a belt rewinding direction. The rotatable part (1) may be an extension of the reel shaft or an independent part couplable in the event of a crash, for example by a clutch (14), to the reel or its shaft. The coupling of such a clutch (14) may be by use of a ramp surface (17) associated with the piston (2) which urges the clutch parts together on actuation of the pretensioner. Preferably two such pistons (2) are arranged on opposite sides of the rotatable part (1). The gas generators (7) are actuated pyrotechnically and may be integral with the piston(s) (2). Generally a smaller pyrotechnic charge is needed to drive the reel than with hitherto known systems. Engagement between the piston(s) (2) and the rotatable part (1) is via abutting surfaces (20, 21) which may be roughened, knurled or splined to engage by friction, or may be toothed to more positively engage. This pretensioner (12) is compact and lightweight and is cheaper and easier to fit to retractors than known pretensioners. It lends itself easily to a modular design and can be replaced quickly and easily, for example after a crash has occurred. It may be mounted in a compact plastic protective housing which can be adapted to the decor of the vehicle.

Description: PRETENSIONER FOR SEAT BELT RETRACTOR DESCRIPTION The present invention relates to a pretensioner for a seat belt retractor. Pretensioners wind in belt slack in the event of a vehicle crash so as to restrain a passenger more securely reducing belt injuries and to ensure that the passenger is optimally oriented in a seat when a gas bag is inflated (when fitted) . Known methods of pretensioning include using a piston, driven either by a spring or by pyrotechnic means, to pull a cable wound round the belt retractor reel in the event of a crash. Large forces are needed due to the inertia of the retractor and because it is necessary to effect the pretensioning in the first milliseconds of a crash situation i.e. before the belt is tensioned by the passenger's forward movement in the crash. These known systems are heavy and bulky. The piston/cylinder arrangement may be close-coupled to the retractor but problems are encountered in fitting such a retractor system in the limited space available between a seat and the side of a car. On the other hand if the piston/cylinder arrangement is located remote from the reel so that it can be fitted in a convenient space in a car, e.g. to the chassis under a seat, then an unwieldy length of cable is required, adding to expense in production and decreasing efficiency. In addition, known systems require complex and costly clutch arrangements to engage effectively with the retractor reel within the required time scale. It is an object of the present invention to provide a more compact and lightweight pretensioner reel retractor which can be easily fitted in a vehicle. According to the present invention there is provided a pretensioner arrangement for a vehicle safety restraint retractor for winding a seat belt retractor reel in a belt rewinding direction in the event of a crash, the pretensioner comprising: at least one linearly movable positive displacement member; driving means for moving the member along a predetermined path, the member having a surface portion adapted to engage a corresponding peripheral surface on a rotatable part so as to transfer the linear momentum of the member to rotary momentum of the rotatable part; and means for coupling the rotatable part of the belt reel on the occurrence of a crash so that the pretensioner winds the reel in a belt rewinding direction. In normal operation, i.e. normal unwinding and inertial rewinding of the retractor reel, the linear displacement shaft engaging member is spaced from the shaft. However means actuable in a crash situation are provided to bias the member into engagement with the shaft. Such means may take the form of a spring or alternatively a solenoid, or a gas cushion which may itself be generated by the gas generator used to move the or each engaging member. According to a preferred embodiment of the present invention there are two shaft engaging members mounted so that in a crash situation they are driven longitudinally in parallel opposite directions so as to reinforceably co-operate in rotating the reel shaft and thus rewind the reel. The two shaft engaging members may be driven by a common gas generator or by separate gas generators or alternatively the exhaust gases from the first driven member may be used to drive the second member. Preferably, a substantial part of the retractor reel, for example the spool and the supports, is formed of a plastics material or other light yet generally strong material so as to reduce the inertia of the reel and reduce the force needed to rewind it. This inertial reduction is further enhanced if the shaft of the reel is small, e.g. less than 8mm diameter. The shaft engaging members may be located in a plastic cartridge which can be easily fitted to a reel in a vehicle by sliding it over the shaft extension. For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Fig. 1 is a cross-sectional view of a pretensioner according to one embodiment of the invention; Fig. 2 shows a cartridge containing a pretensioner according to the present invention; Fig. 3 is a cross-sectional side view of a second embodiment of the invention; Figs. 3A are views in the direction of arrow A of Fig. 3 illustrating the engagement of the piston with the clutch; Figs. 3B are front views of Fig. 3 in the direction of arrow B; Figs. 4a-c are sequence diagrams illustrating the operation of the pretensioner of Fig. 3; and Fig. 5 is a side view of an alternative piston shape. The extension of a retractor reel shaft is shown at 1, and two co-operating shaft engaging rods 2 are biased against the shaft extension 1 by springs 3 in a pretensioning situation as shown in the Figure. The shaft engaging rods are located in cylinders 4 which guide them for movement in longitudinal directions as indicated by arrows 5. The engaging rods 2 have roughened planar surfaces 6 on the sides which (in use) abut the shaft extension. They are driven by gas generators 7 detonated electrically via wiring 8 connected to a vehicle sensor for detecting a crash situation and generating an electrical signal in response thereto. About lOOmg of explosive may be sufficient to drive the rods 2 enough to rotate the shaft 1 to rewind the reel the required amount (i.e. to rewind the belt webbing by at least 28cm) provided the reel spool and supports are made of plastic material. Hitherto quantities of 400-1400mg explosive have been needed in traditional piston cylinder pretensioning systems. The shaft extension typically has a diameter of 8mm and rotation of the spool can be effected within 10ms. Fig. 2 shows an outer plastic casing 9 surrounding the pretensioner of Fig. 1 which is made of plastic and fitted over the shaft extension 1 through hole 10. Wires 8, connected to respective gas generators protrude from the cartridge casing 9 for connection to a vehicle crash sensor which may be of any one of several well known constructions. It will be seen that a cassette of the form shown in Fig. 2 is easily fitted to a retractor in a vehicle. After the pretensioning operation is effected, a web clamp prevents the belt from unwinding from the reel in response to the force of a passenger against the belt as the vehicle decelerates in a crash situation. Such a web clamp is known and serves to lock clamping wedge shaped jaws against the belt webbing to prevent unwinding and keep the passenger safely and firmly located upright in the seat. In Fig. 3 a retractor webbing spool 11 has a compact pretensioner 12 attached at one side and is separated therefrom in normal retractor use by the action of a spring 13. The spring 13 urges apart two plates of a friction or teeth clutch, indicated generally at 14. The pretensioner 12 comprises a central knurled or toothed spindle 15 mounted to pretensioner clutch plate 14, and two pistons 16 mounted on either side of and in close proximity to the spindle 15. In the event of a crash situation, as detected by a vehicle sensor, the pretensioner 12 is activated to rewind loose webbing onto the spool. This is done by engaging the clutch 14 and driving pistons 16 in opposite directions to rotate the spindle 15 and consequentially the spool 11 in a webbing rewind direction. The engagement of the clutch 14 is illustrated in Figs. 3A which are views in the direction of arrow A. The tip of each piston 16 has a lateral cut out portion providing a ramp surface 17 and an abutment surface 18. The left hand drawing in Fig. 3A shows the position with the piston stationary and the clutch open. As the piston begins to move (as in the right hand drawing) the clutch is urged into a closed position. The roughened, knurled, splined or toothed areas 20 of the pistons then begin to engage similar surfaces 21 on the pretensioner spindle 15 and cause the spindle and through the clutch, the spool, to rotate. Figs. 3A and 3B similarly show stationary pistons and disengaged clutch position to the left, and moving pistons with the clutch closed and the pistons beginning to push the start of rotation, to the right. Fig. 3B illustrates a further advantageous embodiment of the invention wherein the pretensioner spindle 15 has radially extending arms 19 which provide for an initial positive engagement for the pistons with the spindle and give the motion a push or kick start. This is illustrated more clearly in the sequence diagram of Figs. 4a, b, c. Fig. 4a shows the abutment surface 18 of each piston engaging the arms 19 and pushing the spindle 15 in an anti-clockwise direction. Subsequently (as in Fig. 4b) the pistons engage the friction surfaces 21 and frictionally rotate the spindle further. Fig. 4c shows the completion of the piston stroke. Fig. 5 shows an alternative shaped piston which provides for a double kick start since a second slot 22 is positioned along its length to engage the second radial arm to provide a second positive engagement and push during the piston stroke. Of course more than two arms may be provided for the spindle and the position of the second piston slot 22 would be adjusted accordingly. A trailing ramp edge 23 is shown on this piston to provide for cpntrolled clutch release at the end of the stroke. of course, the position of this surface has to be carefully adjusted. The pistons are preferably gas driven either by including integral gas generators which move with the pistons or by using the propulsion force of a stationary gas generator to push the piston. The gas generator may be arranged to cause a gas cushion to develop on the outer axial side of the piston to urge the piston into engagement with the spindle. Gas generators may be arranged to burn simultaneously or in sequence to propel the pistons together or one after the other.

Claims: CLAIMS 1. A pretensioner arrangement for a vehicle safety restraint retractor for winding a seat belt retractor reel in a belt rewinding direction in the event of a crash, the pretensioner comprising: at least one linearly movable positive displacement member; driving means for moving the member along a predetermined path, the member having a surface portion adapted to engage a corresponding peripheral surface on a rotatable part so as to transfer the linear momentum of the member to rotary momentum of the rotatable part; and means for coupling the rotatable part of the belt reel on the occurrence of a crash so that the pretensioner winds the reel in a belt rewinding direction. 2. A pretensioner according to claim 1, wherein the reel is mounted on a shaft and an axial shaft extension is arranged to abut the linear displacement member in a crash situation so that the member directly drives the reel by co¬ operation of the engagement surfaces. 3. A pretensioner according to claim 1, wherein the coupling means comprises a clutch and movement of the displacement member in response to a crash situation is arranged to engage the clutch. 4. A pretensioner according to claim 3, wherein the displacement member is shaped with a leading end having a ramp surface which engages a clutch control member to bring the clutch into engagement as the piston moves in a pretensioning operation. 5. A pretensioner according to claim 3 or 4, wherein the displacement member has a tapering cam surface at its trailing end for effecting controlled disengagement of the clutch. 6. A pretensioner according to any preceding claim comprising means for guiding the linearly displaceable member in a direction tangential to the rotatable part. 7. A pretensioner according to any preceding claim comprising two linearly displaceable members for rotating the rotatable part and arranged to be driven in opposing tangential directions relative to the rotatable part. 8. A pretensioner according to any preceding claim, wherein the driving means comprises a gas generator arranged to linearly drive the displacement member. 9. A pretensioner according to claim 8, wherein the gas generator is mounted to move with the displacement member. 10. A pretensioner according to claim 7, wherein the driving means comprises two gas generators arranged for driving respective displacement members. 11. A pretensioner according to claim 7 wherein the driving means comprises one gas generator arranged to drive both displacement members simultaneously. 12. A pretensioner according to claim 10 comprising synchronising control means for controlling the firing of the two gas generators in sequence. 13. A pretensioner according to claim 7 comprising means for connecting the two displacement members so that exhaust gases, from firing the gas generator for driving the first member act on the second member to impart driving force thereto. 14. A pretensioner according to any one of claims 8 to 13 comprising pyrotechnic firing means for the or each gas generator. 15. A pretensioner according to any preceding claim, wherein the engagement surfaces co-operate by friction to transfer movement of the rotatable part. 16. A pretensioner according to claim 15, wherein the engagement surfaces are knurled. 17. A pretensioner according to claim 15, wherein the engagement surfaces are roughened. 18. A pretensioner according to claim 15, wherein the engagement surfaces are splined. 19. A pretensioner according to any preceding claim, wherein the engagement surfaces are toothed to provide a positive engagement. 20. A pretensioner according to any preceding claim, wherein the rotatable part has at least one radially extending arm and the displacement member has an abutment surface arranged to engage the arm during the pretensioning operation so as to drive the rotatable part. 21. A pretensioner according to claim 20, wherein the displacement member has two such abutment surfaces for engaging different or the same arms of the rotatable part. 22. A. pretensioner according to any preceding claim comprising means for biasing the or each displacement member towards and ,into engagement with the rotatable part in response to a crash situation. 23. A pretensioner according to claim 22, wherein the biasing means comprises a spring located at the leading tip of the displacement member. 24. A pretensioner according to claim 22, wherein the biasing means comprises a solenoid actuable on a crash being detected. 25. A pretensioner according to claim 22, wherein the biasing means comprises a gas cushion generated in response to a crash being detected. 26. A pretensioner according to any preceding claim which is removably connected to a retractor. 27. A pretensioner according to any one of the preceding claims in combination with a web clamping device located at the webbing payout side of the retractor. 28. A pretensioner according to any one of the preceding claims when fitted to a retractor with a reel made substantially of plastics material.

Inventors: AISTON BRIAN, AISTON, BRIAN
Applicants: AISTON BRIAN, ALLIEDSIGNAL LTD, AISTON, BRIAN, ALLIEDSIGNAL LIMITED
Application year: 1995
Main classification: B60R22
IPC codes: B60R22