GB2237180A - A seat belt pre-tensioner arrangement - Google Patents

Abstract

The arrangement is adapted to apply tension to a safety bed via the shaft 6 of a reel upon which the belt is wound. It operates in response to severe deceleration of a vehicle and comprises a helical spring (10, Fig. 1) which is normally retained in a compressed state by a releasable stop 32 and a mechanical trigger 11 for releasing the stop thereby enabling the spring to expand and apply a force to the shaft of the reel so as to rotate the shaft and apply tension to the seat belt. The trigger includes an inertia mass 42 mounted on a lever 43 having an arm 45 which, in an emergency, trips the over-centre mechanism 38, 40 to move a restraining member 35 away from the stop 32. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO A SEAT BELT PRE-TENSIONER ARRANGEMENT The present invention relates to a seat belt pretensioner arrangement.

It has been proposed previously to provide, in a vehicle such as a car, a seat belt pre-tensioner which is an arrangement adapted to apply a positive tension to the seat belt in the event that an accident arises.

Such a pre-tensioner comprises means to applv tension to the seat belt or to a fitting associated with the seat belt and means to initiate operation of the device in response to an accident occurring.

Previous arrangements have included proposals whereby tension is applied to the seat belt via the seat belt buckle into which a tongue upon which the belt is carried is inserted and proposals whereby tension is applied to the belt via the shaft of a reel upon which the belt is wound. Reference may be made, for example, to French Patent Application No. 7806727, Publication No. 2382903 which discloses a pre-tensioner arrangement which tensions a safety belt via a buckle. The arrangement incorporates either a pyrotechnic device or a helical spring which serves to draw the buckle in a downwards direction in the event of an accident thereby applying tension to the belt. Such arrangements are far from ideal.Firstly, applying tension to the belt via the belt buckle entails tensioning the safety belt primarily in the lap region of the wearer and therefore does not tend to pull the upper part of the belt wearer's body back into his seat. Thus with an arrangement which operates via the belt buckle the head of a person wearing the safety belt may still be thrown forward in an accident by a sufficient distance for the persons head to hit the steering wheel or the dashboard.

Clearly this is a most undesirable situation. It is also possible that upon actuation of the pre-tensioner the shock applied to the buckle by the pyrotechnic device or the spring may cause the tongue carrying the belt to become disengaged from the buckle unless the buckle is specifically designed to withstand such a shock. In this case the seat belt would provide no restraint whatsoever for the wearer. If the pretensioner arrangement is to operate via the seat belt buckle then clearly sufficient space must be provided within the motor vehicle to allow for movement of the buckle in order to tension the belt.

In view of the above-mentioned problems and disadvantages, it is considered more acceptable to have a pre-tensioner arrangement which applies tension to the safety belt via the reel upon which the belt is wound.

This avoids any risk of the tongue carrying the belt becoming disengaged from the seat belt buckle and also serves to restrain the upper part of the belt wearers body and in particular the head in accident conditions, since the belt usually passes from the reel across the chest of the wearer via a shoulder strap portion.

The use of pyrotechnic devices in pre-tensioner arrangements is also somewhat hazardous since the pyrotechnic devices can emit a very loud noise when actuated. The pyrotechnic devices are also hazardous to manufacture and to dispose of.

French Patent Application No. 7806727 referred to above also discloses a pre-tensioner arrangement which applies tension to the safety belt via the reel upon which the belt is wound. However, the arrangements proposed are operated by way of a pvrotechnic device or by means of a spiral spring acting upon the reel shaft.

It is to be noted that the use of spiral springs is relatively common in this field where it is desired to rotate the shaft of a seat belt reel.

All the arrangements disclosed in the French Specification have their disadvantages. Each of them requires an electrical signal to be generated in response to an accident occurring, this electrical signal either triggering an explosive or operating a solenoid forming part of a release trigger. It takes a period of time, albeit a brief period of time, for an electrical signal to trigger an explosive or to actuate a solenoid. It is to be appreciated that if a seat belt pre-tensioner is to be of value it is important that the tension is applied to the seat belt as soon as an accident is detected. If there is any delay, even a very short delay, the tension may be applied to the seat belt too late to be of any real value.

It is also possible that in an accident the vehicle electrical supply may fail if wires become cut or broken or if a fuse blows. Thus it is not really desirable to have to rely on the vehicle electrical supply being operational in order for the pre-tensioner arrangement to work.

The present invention seeks to provide an improved pre-tensioner arrangement which operates in a satisfactory and reliable manner but which is relatively economic to manufacture.

According to the present invention there is provided a pre-tensioner arrangement adapted to apply tension to a safety belt via the shaft of a reel upon which the belt is wound, the arrangement operating in response to severe deceleration of a vehicle in which the arrangement is fitted, the arrangement comprising force storing means in the form of a helical spring, the spring being adapted, when released, to apply a force to the shaft of the reel, means being provided to retain the spring in a compressed state; and a mechanical trigger for releasing the spring in response to severe deceleration of the vehicle.

Although French Specification No. 2382903 discloses the use of a helical spring in relation to a pre-tensioner, this is only in relation to a pretensioner which tensions a safety belt via the belt buckle and not via the belt reel. The helical spring associated with the buckle in the French Specification has a triggering arrangement which also requires an electrical signal in order to be released. Whilst the French specification teaches the use of a spiral spring acting on the belt reel instead of a pyrotechnic device, it is apparent that the inventors of the pre-tensioner arrangement in the French Specification had not contemplated the use of a helical spring acting on the belt reel and being triggered mechanicallv.

The arrangement of the present invention has numerous advantages. In particular, experiments have shown that the mass of a cylindrical section helical spring is less than that of a flat spiral spring if the springs are to deliver the same force for the same spring extension. Thus, a lighter, helical spring may be used to produce the same force as a heavier spiral spring. The overall mass of the arrangement is therefore reduced. A helical spring is also more economic to manufacture than a spiral spring and thus the overall cost of the pre-tensioner arrangement is reduced. The reliability of the arrangement is optimised by using a purely mechanical trigger since no reliance is placed upon the electrical supply being operational.

Preferably the mechanical trigger comprises a lever adapted to engage part of the pre-tensioner arrangement for retaining the spring in the compressed condition and an over-dead-centre linkage which normally holds the lever in position engaging said part of the pre-tensioner arrangement, the over-dead-centre linkage being movable under accident conditions to release the lever and enable the spring to expand, thereby applying a force to the reel shaft which rotates the shaft and applies tension to the safety belt.

Conveniently the trigger incorporates an inertia mass adapted to move in a predetermined way when subjected to severe deceleration, the inertia mass having means thereon adapted to engage the over-deadcentre linkage and to move the over-dead-centre linkage through the dead-centre condition so as to release the lever.

Advantageously the over-dead-centre linkage comprises two links, the means on the inertia mass which are adapted to engage the linkage being adpated to engage said two links substantially at or adjacent their point of connection.

Preferably the links comprising the over-deadcentre linkage are interconnected to articulate in a substantially friction-free manner.

Conveniently each link of the linkage is provided with a substantially knife edge or pointed end which is received within an appropriate recess so as to constitute a substantially friction-free articulation.

Advantageously the inertia mass is mounted upon a shank, the shank being aligned with a point about which the inertia mass rotates when subjected to said severe deceleration, the shank having a cranked extension to engage the over-dead-centre linkage.

Preferably the inertia mass is mounted for pivotal or tilting movement about a point which is offset from the point at which the means to engage the over-dead-centre linkage actually engage that linkage.

Conveniently said lever comDrises a pivotally mounted member defining, on one side of the pivot axis thereof, an abutment face for engaging said part of the pre-tensioner arrangement, and defining on the other side of the pivot axis thereof a portion to engage said over-dead-centre linkage.

Advantageously the helical spring is connected to the shaft of the reel under accident conditions via a cable and a clutch device, one end of the cable being attached to a stop which forms said part of the pretensioner arrangement adapted to be engaged by said lever.

Preferably the stop carries a rod, the free end of the rod being attached to a plunger which is engaged by one end of the helical spring, the arrangement being such that when the lever is released from the stop the spring moves the plunger and the cable which is connected thereto via the stop and the rod, movement of the cable actuating the clutch device such that a connection is formed with the reel shaft.

Conveniently the clutch device comprises an extension of the reel shaft and a plurality of shoes mounted around the extension of the reel shaft at poisitons spaced therefrom, the shoes being movable into non-slipping engagement with the extension of the reel shaft, the cable being wound around the outer peripherary of the shoes, tension applied to the cable serving to move the shoes into engagement with the extension of the shaft of the reel.

Advantageously the shoes are biassed to the disengaged position.

Preferably the shoes are biassed to the disengaged position by means of spring elements formed integrally with the shoes.

Conveniently the shoes are pivotally mounted in the clutch device, each shoe being of generally arcuate form and being pivotally mounted adjacent one end thereof.

Advantageously the shoes are pivotally mounted at their trailing edges considered in the sense of the direction of rotation of the shoes when tension is applied to the cable.

Preferably the shoes are pivotally mounted on pivot pins which have axes extending parallel with the axis of the shaft of the belt reel, the pivot pins being mounted on a ring-shaped element, means being provided initially to retain the ring-shaped element in a predetermined position.

Conveniently said means to retain the ringshaped element in a predetermined position comprise narrow necks of material joining the ring-shaped element to a further part of the structure of the clutch device, the necks of material being frangible.

In order that the present 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 schematic side view, partly in section, of a seat belt pre-tensioner arrangement in accordance with the present invention; FIGURE 2 is an end view of the arrangement shown in Figure 1; FIGURE 3 is an end view of a clutch device forming part of the pre-tensioner arrangement; and FIGURE 4 is an enlarged view of part of Figure 1 illustrating a trigger device of a pre-tensioner more clearly.

Referring to Figures 1 and 2 of the accompanying drawings, a safety belt pre-tensioner arrangement comprises a conventional retractor reel assembly 1 which incorporates a shaft portion 2 on which a safety belt may be wound and which also incorporates a cover 3 covering a locking mechanism for locking the shaft 2 under predetermined accident conditions. The retractor reel assembly is provided with a mounting plate 4 provided with apertures 9 to receive mounting bolts for mounting the retractor reel assembly on the chassis of a motor vehicle. The retractor reel assembly also incorporates a spring to apply a rotational force to the shaft 2. As thus far described the retractor reel assembly may be of conventional design.

One end of the shaft 2 is extended to form an extension 6. The outer surface of the extension 6 carries teeth 7 spaced around its circumference and extending longitudinally along the extension.

The teeth 7 of the extension 6 forms part of a clutch device illustrated in Figure 3 of the drawings, the clutch device serving, under accident conditions, to connect an element upon which a cable or wire 8 is wound to the extension 6 of the shaft 2 such that tension applied to the cable 8 causes rotation of the shaft 2.

The clutch device will be described in further detail hereinafter.

The cable 8 is connected to a pre-tensioner arrangement 9 comprises force storing means in the form of a helical spring 10 which is normally retained in a contracted state but may be released by a mechanical trigger 11 in order to apply tension to the cable 8 which in turn rotates the shaft 2 by way of the clutch device referred to above.

Looking at the various components in more detail, the clutch device, illustrated in Figure 3, comprises a housing 12 incorporating a central, circular chamber 13 and a guide channel 14 through which the cable 8 may enter the chamber 13. The chamber 13 is dimensioned to receive the extension 6 of the shaft 2 and to this end the base of the chamber 13 is provided with a central aperture 15 through which the extension of the shaft 2 may pass.

The base of the chamber 13 is formed with an inner, annular portion 16 which surrounds the aperture 15 and which is separated from the rest of the base by a plurality of arcuate slots 17, so that the annular portion 16 is only connected to the rest of the base by three relatively narrow necks of material 18. The inner, annular portion 16 carries three equi-angularly spaced, upstanding pivot pins 19.

An integrally moulded, plastics shoe and spring assembly 20 is provided within the chamber 15, the assembly comprising three shoe portions 21 which are inter-connected by relativelv narrow webs 22 which comprise biassing springs which serve to bias the shoes radially outwardly, i.e. away from the outer surface of the extension 6 of the shaft 2. It is to be noted that the radially innermost surface of each shoe 21 is formed with teeth 23 which are designed to cooperate with and form a non-slipping engagement with the teeth 7 of the extension 6 of the shaft 2. Each shoe portion 21 is pivotally mounted upon a respective pin 19 by way of an aperture or recess 24 formed therein. The apertures or recesses 24 are each located adjacent one end of a respective shoe portion. Each shoe portion is of arcuate form and, when mounted upon a respective pivot pin 19 is located adjacent the extension 6 of the shaft 2. The axes of the pivot pins 19 are parallel with the axis of the shaft 2.

As can be seen from Figure 3 the cable 8 from the pre-tensioner arrangement passes, with several turns, around the outsides of the shoe portions 21, the cable being received in grooves 25 defined in the rear surfaces of the shoes. The free end of the cable is provided with an enlargement or stop 26 which engages an abutment face 27 defined on the appropriate shoe portion. Thus, the free end of the cable 8 is connected to one of the shoes 21.

The shoes 21 are normallv in the position illustrated in Figure 3 of the drawings in which they do not engage the extension 6 of the shaft 2. When tension is applied to the cable 8, initially the tension in the cable serves to cause each shoe 21 to pivot about the respective pivot pin 19, against the bias provided by the spring elements 22, so that the inner surface of each shoe carrying the teeth 23 is brought into nonslipping engagement with the teeth 7 of the extension 6 of the shaft 2. The shoes are thus in an engaging position.Further tension will tend to cause the inner, annular portion 16 to rotate in an anti-clockwise direction, and eventually the narrow necks 18 of material will break thus enabling the annular portion 16 carrying the pivot pins 19 to rotate about the axis of the shaft 2, thus causing the shaft to rotate by virtue of the engagement of the shoes 21 with the teeth 7 of the extension 6.

Tension is applied to the cable 8 under accident conditions by way of the helical spring 10.

The helical spring 10 is retained, normally in a compresses state, in a cylindrical housing 28 and extends between an end cap 29 formed integrally with the housing at one end thereof and a plunger 30 which is slideably received in the housing 28. When the spring 10 is compressed the plunger 30 is located adjacent the opposite end of the housing to the cap 2 and that end of the housing, i.e. the end at which the plunger 30 is located, is an open end. One end of a rod 31 is mounted centrally on the plunger 30 and extends along the length of the housing, within the spring 10, passing through an aperture formed centrally in the end cap 29. The rod therefore passes out through the bottom of the housing 28 and is formed at its end with an enlarged stop 32 to which the end of the cable 8 which emerges from the clutch device is attached.

The stop 32 cooperates with the mechanical trigger 11 so as normally to retain the spring 10 in the compressed condition. The trigger 11 is contained within a fixed housing 33 located adjacent the enlarged stop 32. Pivotally mounted on the housing 83, about a pivot axis 34, is a restraining member 35, which defines an abutment surface 36 which, in one pivotal position of the restraining member engages one end face of the enlarged stop 32, thus preventing the rod 31 from moving under the bias applied thereto by the compression spring 10.At a further position on the restraining member 35, on the opposite side of the axis of pivoting thereof, is a recess 37 in which is received one end, which presents a knife edge or a point, of an elongate member 38 which defines, at its other end, a recess 39 which receives one end of a further elongate member 40. The end of the elongate member 40 which engages in the recess 39 may also present a knife edge or a point. The other end of the further elongate member 40 is recessed and engages an abutment 41 formed on the housing 33. The abutment 41 may also be in the form of a knife edge or a point.

The arrangement is such that the elongate members 38,40 form a two-part link which is in an over-dead-centre condition, the point of connection between the knife edge and of the member 40 and the recess 39 on the member 38 being off-set from a straight line between the projection 41 and the recess 37. The links are all associated with low-friction articulations defined by the knife edges or points received in the respective recesses.

An inertia mass 42 is provided, the mass being mounted upon a shank 43 which is pivotal about a pivot point 1414. There is a lateral extension 45 of the shank 43, which extends perpendicularly to the axis of the main portion of the shank. The extension 45 engages the two links 38,40 in the region of their central point of connection. The inertia mass 42 is restrained from moving in the direction of the arrow 46 by means of a stop 47, but is free to move in the direction of the arrow 148.

The arrangement, as described above, is mounted in a motor vehicle which is intended to travel in the direction of the arrow 48. If the vehicle is involved in an accident such that the driver of the vehicle or a passenger in the vehicle is to be restrained in their seat, then the vehicle will suffer severe deceleration as considered in the direction of movement as indicated by the arrow 148. The inertia mass 42 will, under such conditions, continue to move forward, relative to the remainder of the described arrangement, in the direction of the arrow 48. The inertia mass 42 will thus pivot about the pivot point 44 which engages the shank 43 and the projection 45 will thus move the point of connection of the two links 38,40 through the dead-centre condition and the two links will then be freed from each other and from the rest of the apparatus.

The restraining member 35 will then be free to rotate about the axis 34 in a clockwise direction as viewed in Figure 14. Rotation of the restraining member 35 will disengage the abutment surface 36 from the enlarged stop 32 and consequently the force applied to the plunger 30 by the compression spring 10 will move the plunger upwardly, as seen in Figure 1. As the plunger moves upwardly tension will be applied to the cable 8 which will cause the shoes 21 to engage the teeth 7 of the extension 6 of the reel shaft 2 and the reel shaft will be rotated as the spring 10 expands thereby retracting part of the safety belt onto the reel, this retraction serving to restrain the wearer of the belt within his seat in the motor vehicle in which the pre-tensioner arrangement is fitted.

It will be appreciated that various modifications may be made to items such as the clutch device and the mechanical trigger without departing from the scope of the present invention.

Claims (20)

1. A pre-tensioner arrangement adapted to apply tension to a safety belt via the shaft of a reel upon which the belt is wound, the arrangement operating in response to severe deceleration of a vehicle in which the arrangement is fitted, the arrangement comprising force storing means in the form of a helical spring, the spring being adapted, when released, to apply a force to the shaft of the reel, means being provided to retain the spring in a compressed state; and a mechanical trigger for releasing the spring in response to severe deceleration of the vehicle.

2. A pre-tensioner arrangement according to Claim t- wherein the mechanical trigger comprises a lever adapted to engage part of the pre-tensioner arrangement for retraining the spring in the compressed condition and an over-dead-centre linkage which normally holds the lever in position engaging said part of the pre-tensioner arrangement, the over-dead-centre linkage being movable under accident conditions to release the lever and enable the spring to expand, thereby applying a force to the reel shaft which rotates the shaft and applies tension to the safety belt.

3. A pre-tensioner arrangement according to Claim 2 wherein the trigger incorporates an inertia mass adapted to move in a predetermined way when subjected to severe deceleration, the inertia mass having means thereon adapted to engage the over-dead-centre linkage and to move the over-dead-centre linkage through the deadcentre condition so as to release the lever.

4. A pre-tensioner arrangement according to Claim t wherein the over-dead-centre linkage comprises two links, the means on the inertia mass which are adapted to engage the linkage being adapted to engage said two links substantially at or adjacent their point of connection.

5. A pre-tensioner arrangement according to Claim 4 wherein the links comprising the over-dead-centre linkage are interconnected to articulate in a substantially friction-free manner.

6. A pre-tensioner arrangement according to Claim 5 wherein each link of the linkage is provided with a substantially knife edge or pointed end which is received within an appropriate recess so as to constitute a substantially friction-free articulation.

7. A pre-tensioner arrangement according to any one of Claims 2 to 6 wherein the inertia mass is mounted upon a shank, the shank being aligned with a point about which the inertia mass rotates when subjected to said severe deceleration, the shank . having a cranked extension to engage the over-dead-centre linkage.

8. A pre-tensioner arrangement according to any one of Claims 2 to 7 wherein the inertia mass is mounted for pivotal or tilting movement about a point which is offset from the point at which the means to engage the over-dead-centre linkage actually engage that linkage.

9. A pre-tensioner arrangement according to any one of the preceding Claims wherein said lever comprises a pivotally mounted member defining, on one side of the pivot axis thereof, an abutment face for engaging said part of the pre-tensioner arrangement, and defining on the other side of the pivot axis thereof a portion to engage said over-dead-centre linkage.

10. A pre-tensioner arrangement according to any one of the preceding Claims wherein the helical spring is connected to the shaft of the reel under accident conditions via a cable and a clutch device, one end of the cable being attached to a stop which forms said part of the pre-tensioner arrangement adapted to be engaged by said lever.

11. A pre-tensioner arrangement according to Claim 10 wherein the stop carries a rod, the free end of the rod being attached to a plunger which is engaged by one end of the helical spring, the arrangement being such that when the lever is released from the stop the spring moves the plunger and the cable which is connected thereto via the stop and the rod, movement of the cable actuating the clutch device such that a connection is formed with the reel shaft.

12. A pre-tensioner arrangement according to Claim 10 or 11 wherein the clutch device comprise an extension of the reel shaft and a plurality of shoes mounted around the extension of the reel shaft at positions spaced therefrom, the shoes being movable into non-slipping engagement with the extension of the reel shaft, the cable being wound around the outer peripherary of the shoes, tension applied to the cable serving to move the shoes into engagement with the extension of the shaft of the reel.

13. A pre-tensioner arrangement according to Claim 12 wherein the shoes are biassed to the disengaged position.

114. A pre-tensioner arrangement according to Claim 13 wherein the shoes are biassed to the disengaged position by means of spring elements formed integrally with the shoes.

15. A pre-tensioner arrangement according to any one of Claims 12 to 14 wherein the shoes are pivotally mounted in the clutch device, each shoe being of generally arcuate form and being pivotally mounted adjacent one end thereof.

16. A pre-tensioner arrangement according to Claim 15 wherein the shoes are pivotally mounted at their trailing edges considered in the sense of the direction of rotation of the shoes when tension is applied to the cable.

17. A pre-tensioner arrangement according to Claim 15 or 16 wherein the shoes are pivotally mounted on pivot pins which have axes extending parallel with the axis of the shaft of the belt reel, the pivot pins being mounted on a ring-shaped element, means being provided initially to retain the ring-shaped element in a predetermined position.

18. A pre-tensioner arrangement according to Claim 17 wherein said means to retain the ring-shaped element in a predetermined position comprise narrow necks of material joining the ring-shaped element to a further part of the structure of the clutch device, the necks of material being frangible.

19. A pre-tensioner arrangement substantially as herein described with reference to and as shown in the accompanying drawings.

20. Any novel feature or combination of features disclosed herein.