A SEAT BELT PRE-TENSIONING DEVICE

Abstract: A seat belt pre-tensioning device is adapted to be mounted on a vehicle and includes a buckle (12) to receive a seat belt buckle. The device incorporates means (28, 50, 60) which are responsive to a predetermined deceleration of the vehicle and which move to permit spring-loaded means (23, 48) to apply a force to move the buckle (12) to apply a tension to the seat belt means.

Description: THIS INVENTION relates to a seat belt pre-tensioning device, and more particularly to a seat belt pre-tensioning device adapted to tension a seat belt when an accident occurs. When an accident occurs involving a motor car it is not unusual for the motor car to be decelerated very rapidly, and in some cases the car can be considered to stop virtually instantaneously. When this happens the occupants of the vehicle, who have their own momentum which is related to the speed of the car before the accident, do not stop immediately, but tend to continue to travel forwardly. It is to arrest this forward movement, and to prevent the occupants of the car from colliding with parts of the car that are now stationary, such as the steering wheel, that seat belts are worn. It is now common for seat belts fitted with inertia reels to be worn. The inertia reel tends to reel up any slack in the seat belt when it has been positioned to restrain the occupant of the car, but is designed to "lock" when subjected to a deceleration in excess of a predetermined deceleration. The inertia reel is thus prevented from rotating to pay out the seatbelt. If a car fitted with such inertia seat belts is involved in an accident, when the car is decelerated rapidly the occupants of the car will still tend to move forwards as a consequence of their own personal momentum. During a brief initial time period the seat belt which is relatively loosely stretched across the occupant of the car is placed under tension as the occupant moves forwardly relative to the seat. The tension in the belt is applied to the reel of the inertia reel device (which is now "Locked") and an extra length of belt is paid out from the reel as the part of the belt that is wound on the reel is tightened. Thus the occupant of the car still moves forwardly. This can occupy the first 35 milli-seconds or so after the instant of impact, and now the occupant has moved a significant part of the way from the seat to the steering wheel or dashboard. Thus, if the occupant is to be arrested before impact with the steering wheel or dashboard very high retarding forces must be applied to the occupant. These retarding forces must be applied to the occupant of the car in a very short period of time, and thus the retarding forces must be very large if the occupant of the car is to be prevented from impacting with the steering wheel or dashboard. These large forces may thus injure the occupant of the car. It has been realised that the risk of injuring the occupant of a car with the seat belt if an accident occurs can be reduced if the seat belt arrangement is such that the occupant of the car can be decelerated as soon as possible after the accident occurs. This can be achieved if the occupant is always strapped in tightly, with the seat belt under significant tension at all times. However, it is not practicable to adopt this technique if inertia reels are used. DE 3304008 A1 discloses a vehicle seat belt pre-tensioning device which is mounted in a vehicle. Part of the seat belt moves between two fixed elements which are spaced apart in the direction of movement of the seat belt. A torsion bar is provided having a cranked end portion which lies between the two fixed elements. An electrical device is provided to hold the torsion bar in a fixed position. When the torsion bar is released the cranked portion moves between the two fixed elements thus drawing part of the safety belt between the two fixed elements and applying a tension to the belt. The electrical device is triggered by a sensor which responds to a predetermined situation. The arrangement relies on electrical triggering which can be disadvantageous, since such triggering takes a finite time to operate. Also, in an accident situation, the electrical supply system can fail totally, and in this case the apparatus described in DE 3304008 A1 would not function at all. US-A-447017 discloses a device adapted to impart a rotational force to a spool which part of a safety belt is wound. The device consists of a spring adapted to press a threaded element along a threaded extension of the shaft on which the spool is mounted, thus causing the shaft to rotate. A separate pendulum-operated trigger is provided. According to this invention there is provided a vehicle seat belt pre-tensioning device comprising means to mount the device in the vehicle, means to receive part of the seat belt, means adapted to apply a force to move the seat belt receiving means to apply tension to the seat belt and means which normally prevent the force applying means from moving the seat belt receiving means, but which are responsive to a predetermined deceleration, to actuate said force applying means to permit the force applying means to apply the force to move the seat belt receiving means, wherein the said force applying means incorporates a movable element which normaly engages a stop to prevent the force applying means moving the seat belt receiving means, the force applying means incorporating at least one element which is movable relative to said mounting means by its own inertia in response to a predetermined deceleration, movement of said element causing the element which normally engages the stop to be disengaged from the stop thus permitting movement of the seat belt receiving means under a force from said force applying means. Embodiments of the invention do not utilise an electric triggering arrangement. Also embodiments of the invention do not utilise a separate pendulum-operated trigger arrangement. Instead, in embodiments of the invention, the means which apply the force to move the seat belt receiving means incorporate at least one element which is movable by its own inertia in response to a predetermined deceleration, this movement causing the element which normally engages the stop to be disengaged from the stop. Consequently, manufacturing costs can be minimised, since the number of components provided can be minimised, while still providing a very effective pre-tensioning device. Preferably wherein the force applying means incorporate a torsion bar adapted to apply a force to said movable member, the torsion bar being arranged to extend transversely of the vehicle, one end of the torsion bar being connected to said movable element of the device, the said one end of the torsion bar comprising the said element that is movable by its own inertia. Conveniently the said movable element of the device is in the form of a control lever, part of which engages the stop, the control lever being biassed so that when the control lever is disengaged from said stop the control lever will rotate, movement of the control lever causing movement of said seat belt receiving means. Preferably the control lever is biassed by the force applying means. Advantageously the control lever is connected to a movable member to which the seat belt receiving means are connected, the control lever being connected to the movable member by means of a pin and slot connection which permits axial movement of the control lever relative to the movable member, but which transmits rotational movement of the control lever to the movable member. Preferably means are provided for retaining the movable member in the position that it occupies after the force has been applied thereto. In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described by way of example, with reference to the accompanying drawings in which: Figure 1 is a perspective view of the operative parts of one embodiment of a device in accordance with the invention, partly exploded and partly cut-away, Figure 2 is an end elevational view of part of the device of Figure 1, and Figure 3 is an exploded perspective view of the device of Figures 1 and 2, with parts cut-away, showing supporting elements in phantom. Referring to the drawings, one embodiment of a device in accordance with the invention includes a support plate 1, which is mounted in a vertical orientation in a vertical plane aligned with the axis of the car. In the illustrated embodiment mounting bolts or the like pass through apertures 2 formed in the plate 1, and secure the plate 1 to a vertical supporting element 3 which in turn is secured to the body of the car. A first pivot pin 4 extends from one face of the plate 1. An arcuate pivoting member 5 has an aperture 6 therein which receives the pivot pin 4 so that the member 5 is pivotal about the pin 4. The end of the member 5 on one side of the pin 4 is provided with a plurality of serrations or teeth 7. On the other side of the pivot pin 4 the member 5 is provided with an aperture 8 which receives a rivet 9 passing through an aperture 10 in a metal strap 11 extending from a conventional seat belt buckle 12. The seat belt buckle 12 is designed to accommodate a tongue mounted on a seat belt. At a position beyond the aperture 8 the member 5 is provided with a protruding guide pin 13, which protrudes from the face of the planar member 5 which is remote from the plate 1. The plate 1 is provided with a second pivot pin 14 at a position adjacent the serrated end 7 of the member 5 and this pivot pin carries a spring biassed ratchet member 15 which engages the teeth or serrations 7 in such a way that when the member 5 has executed a clockwise pivotal movement about the pivot pin 4, (as indicated by the arrow 31 in Figure 1) the member 5 is prevented from rotating in the anti-clockwise direction. The plate 1 is also provided with an oval aperture 16, the major axis of which is horizontal, and a small projecting ledge 17, having a horizontal upper surface located just below the aperture 16 on the same side of the plate 1 as the pivot pins 4 and 14. The plate 1 has a further pivot pin 18, which carries a roller bearing 19. Projecting from the other side of the plate 1 is an oval cross-sectioned tube 20 which is aligned with the aperture 16 which thus provides access to the interior of the tube. The tube is closed at the end 21 remote from the plate 1. The end 21 of the tube 20 may be supported, and thus it may be connected in some way to a supporting element 22 which corresponds with the supporting element 3. An elongate torsion bar 23 is mounted in the tube 20. At a first end the torsion bar 23 has a square cross-sectioned projecting peg 24 which is retained in a correspondingly shaped aperture formed in the closed end 21 of the tube 20. The torsion bar 23 passes through the tube 20 and projects through the aperture 16. The projecting part of the torsion bar 23 carries a roller bearing 25 which rests on the upper surface of the ledge 17. The protruding part of the torsion bar then terminates with a square cross-sectioned peg 26 which is received in a correspondingly shaped aperture 27 in a control lever 28. The control lever 28 defines an elongate slot 29 which accommodates the guide pin 13 of the member 5. When the described device is in its initial condition the torsion bar is applying a considerable force to the control lever 28, tending to rotate the control lever 28 in a clockwise direction about the end of the torsion bar 23. However, as can be seen from Figure 2, the end 30 of the control lever 28 rests on the bearing 19, thus preventing rotation of the control lever 28. When the described device has been mounted in a motor car, since the plate 1 is vertical and is aligned with the axis of the car, the tube 20 will extend transversely to the axis of the car. If the car is involved in an accident and decelerates with a deceleration in excess of a predetermined deceleration the end of the torsion bar 23 will tend to move forwardly in the slot 16. The reason for this is that the torsion bar itself will have momentum, and, as the car decelerates, the plate 1 will decelerate and the free end of the torsion bar 23 will tend to move forwardly relative to the plate. Since the end of the torsion bar is mounted on the ledge 17 on a low friction bearing 25, the end of the bar will move freely, and since the control lever 28, which is connected to the torsion bar 23, has the end 30 thereof resting on a low friction bearing 19 the control lever will also move freely. As the end of the torsion bar and the control lever move to the left (as seen in Figure 2) the guide pin 13 effectively slides along the slot 29 in the control lever 28. When a predetermined movement has taken place the end 30 of the control lever 28 will become disengaged from the low friction bearing 19, and then the control lever will be caused to rotate rapidly in the clockwise direction, due to the torsional force applied thereto by the torsion bar 23. As the control lever 28 rotates, the walls of the slot 29 will engage the guide pin 13, thus causing the member 5 to rotate rapidly about the pin 4. This will move the seat belt buckle 12 downwardly very rapidly, thus applying a considerable tension to the seat belt that engages the buckle within a very short period of time after an accident occurs. This will retain the occupant of the vehicle in the seat, providing maximum effective time to decelerate the occupant of the car before the occupant of the car collides with the steering wheel or dashboard. As the member 5 rotates about the pin the ratchet member 15 engages the teeth 7 to prevent the member 5 rotating in the opposite direction. Thus, once the described device has operated to place the seat belt under tension, the device is then able to withstand the high forces that may be applied thereto in an accident situation without permitting the buckle 12 to move upwardly. Many modifications may be effected to the above-described embodiment of the invention without departing from the scope of the claims. For example, the peg 24 of the torsion bar 23 may be located in an elongate slot in the closed end 21 of the tube 20, so that in an accident situation the whole of the torsion bar may move forwardly, instead of just one end moving. It may be desirable to retain the torsion bar in its initial position with resilient means such as springs, the resilient bias applied to the torsion bar having to be overcome before the described device will operate.

Claims: A vehicle seat belt pre-tensioning device comprising means (1) to mount the device in the vehicle, means (12) to receive part of the seat belt, means (23) adapted to apply a force to move the seat belt receiving means (12) to apply tension to the seat belt and means (28, 19) which normally prevent the force applying means from moving the seat belt receiving means, but which are responsive to a predetermined deceleration, to actuate said force applying means to permit the force applying means to apply the force to move the seat belt receiving means, characterised in that the said force applying means (23) incorporates a movable element (28) which normaly engages a stop (19) to prevent the force applying means moving the seat belt receiving means, the force applying means incorporating at least one element (23) which is movable relative to said mounting means by its own inertia in response to a predetermined deceleration, movement of said element (23) causing the element (28) which normally engages the stop (19) to be disengaged from the stop (19) thus permitting movement of the seat belt receiving means under a force from said force applying means (23). A vehicle seat belt pre-tensioning device according to Claim 1, wherein the force applying means incorporate a torsion bar (23) adapted to apply a force to said movable member, the torsion bar (23) being arranged to extend transversely of the vehicle, one end of the torsion bar being connected to said movable element (28) of the device, the said one end of the torsion bar comprising the said element that is movable by its own inertia. A device according to Claim 1 or 2, wherein the said movable element (28) of the device is in the form of a control lever, part (30) of which engages the stop (19), the control lever being biassed so that when the control lever (28) is disengaged from said stop the control lever (28) will rotate, movement of the control lever causing movement of said seat belt receiving means (12). A device according to Claim 3, wherein the control lever (28) is biassed by the force applying means (23). A device according to Claim 3 or Claim 4, wherein the control lever (28) is connected to a movable member (5) to which the seat belt receiving means (12) are connected, the control lever (28) being connected to the movable member (5) by means of a pin and slot connection (13, 29) which permits axial movement of the control lever relative to the movable member, but which transmits rotational movement of the control lever to the movable member. A device according to any one of the preceding Claims, wherein means (15) are provided for retaining the movable member in the position that it occupies after the force has been applied thereto.

Inventors: ANDERSSON, STURE ROLAND, HALAND, LARS YNGVE, MOERNER, BENGT OLOF JOHAN STELLAN, Mörner, Bengt Olof Johan Stellan
Applicants: AUTOLIV DEVELOPMENT AKTIEBOLAG
Application year: 1986
Main classification: B60R22
IPC codes: B60R22