GB2325896A

GB2325896A - Pretensioner

Info

Publication number: GB2325896A
Application number: GB9707854A
Authority: GB
Inventors: Alan George Smithson; Joseph Patrick Harte; David Blackadder
Original assignee: AlliedSignal Ltd
Current assignee: Honeywell UK Ltd
Priority date: 1997-04-18
Filing date: 1997-04-18
Publication date: 1998-12-09
Anticipated expiration: 2017-04-18
Also published as: GB0112198D0; GB9707854D0; GB2359284A; GB2359284B; GB2325896B

Abstract

A pretensioner for a vehicle safety restraint retractor comprises a pinion wheel 5 connected to a retractor spool and rotatable so as to wind seat belt webbing onto the spool, driving means 1 for rotating the pinion wheel and force generating means for moving the driving means, the driving means and pinion wheel having at least two sets of cooperating members, one set being more closely spaced than the other. The driving means may be flexible, eg a chain 1, and the first set of cooperating members may be teeth 6 on the pinion wheel engaging the links (11 fig 2) on a first section of chain 8. The second set of cooperating members may be additional teeth 7 on the pinion wheel, axially offset from the first set, engaging with a second of corresponding spaced links or teeth 10 on a second section of the chain. The force generating means may be a gas generator (14 fig 1). The driving member may be guided within a guide channel 2. The driving means may alternatively be a rack (fig 8) or a string of balls (figs 9 and 10) or a series of interlinked hooks (fig 11) or a frangible rack (fig 12) or a series of balls encased in a foam tube (fig 13).

Description

PRETENSIONER DESCRIPTION The present invention relates to a pretensioner and particularly to a pretensioner for a retractor used in safety restraint systems.

Pretensioners are used in such systems to rapidly rewind seat belt webbing onto a retractor reel in the event of a crash.

In this way slack is taken out of the restraint and the vehicle occupant is more securely restrained and more suitably positioned in the seat to optimise the protection.

This is important for the efficient operation of secondary restraints such as airbags.

A known retractor pretensioner is described in DE 32 20 498 to Daimler-Benz. A rack or chain is driven by gas past a toothed pinion wheel so that the chain links or rack teeth engage the teeth on the wheel and drive the wheel round.

The wheel is connected to the retractor spool. In a crash situation a sensor responsive to sudden changes in vehicle speed, activates a gas generator. The gas drives the rack or chain and rotates the pinion wheel. The wheel drives the retractor spool in a belt rewinding direction.

This known retractor pretensioner requires a long rack or chain to rewind sufficient belt webbing and the device is unacceptably large. In addition, a large rack or chain has a relatively large mass and a high force and thus a high pressure gas generator is needed to drive it fast enough to complete the pretensioning operation in the required time period; typically a few milliseconds. High pressure gas generators are expensive and are bulky items and this is undesirable.

The present invention aims to provide an improved retractor pretensioner.

According to the present invention there is provided a retractor-pretensioner for a vehicle safety restraint comprising a preferably flexible driving member, a pinion wheel connectable to a retractor spool for turning the spool to wind seat belt webbing thereon, force generating means for moving the driving member in a path which passes the pinion wheel, to turn the wheel and consequently the spool, wherein the driving member and the pinion wheel have at least two sets of spaced inter-engagement members, the members of one of the sets being more closely spaced than the members of the other set.

Preferably the driving member comprises a flexible chain and the first set of inter-engagement members comprises radially extending teeth on the pinion wheel spaced to engage correspondingly spaced links in chain. The second set may comprise more closely spaced radial teeth on the wheel, axially offset from the first set of teeth.

These are adapted to engage with a second set of correspondingly spaced links in the chain, or correspondingly spaced teeth on the chain, offset from the first set of links.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made to the accompanying drawings in which: Figure 1 is a cross-sectional view of part of a retractor pretensioner according to the present invention; Figures 2 to 6 are cross-sectional views showing the sequence of operation; Figure 7 is a perspective enlarged view of one form of a sprocket wheel shown in Figures 1 to 6; Figure 8 illustrates a second embodiment of the invention; and Figures 9 to 13 are cross-sectional views of embodiments using alternative forms of chain in retractor pretensioners according to the present invention.

In the Figures an elongate flexible member in the form of a chain 1 is contained in a guide channel 2 within a pretensioner housing 13. A gas generator 14 provides gas pressure in chamber 4 located at one end of the guide channel 2 to apply pressure to a sealing plunger 16 at one end of the chain 1 to drive the chain 1 along the guide channel 2. The channel passes tangentially a pinion wheel or sprocket 5 and is sealed on all sides up to the sprocket 5 by seal 15.

The pinion wheel or sprocket 5 has radially extending teeth in two sets 6 and 7 mounted on the wheel, offset from each axially of the wheel in such a manner as to engage with the chain. The construction of the sprocket 5 is shown more clearly in Figure 7. The pinion wheel 5 can be permanently connected to a spool of a retractor 17. This is an advantage in terms of cost, size and reliability.

Alternatively it may be connected and/or disconnected by use of e.g. a clutch (not shown), so that its rotation turns the spool and rewinds webbing onto the retractor 17.

The chain 1 is of a constant pitch and is in two sections. The upstream section 8 has extended link pins 11 which connect with teeth 6 of the sprocket 5. The first pin 12 is truncated to a semi-circle to allow engagement to any angular position of the sprocket. The second section 9 has teeth 10 which connect with teeth 7 of the sprocket 5. The construction of the chain in this way allows very easy tailoring of the number of extended pins 11 and teeth 10, and also the facility to add a section of extended pins after the teeth 10 to allow a change from lo-hi-lo ratio.

Thus (referring to Figure 2) as the gas pressure in chamber 4 builds, the chain 1 is pushed along the guide channel 2 towards the pinion wheel 5. The first chain link engages the large outer pinion wheel teeth 6, driving the wheel 5 round in an anti-clockwise direction (in the illustrated example) at a rate dependent on the velocity of the chain and the spacing of wheel teeth 6. Typically this would be about 5 /mm at this stage.

As the chain 1 moves along the guide channel 2 the second section 9 of the chain approaches the wheel 5. This is shown in Figure 3. The leading tooth 11 of the second section 9 of the chain is engaged by the smaller inner teeth 7 of the wheel 5. This effectively gears up the system and increases the rate of rotation of the wheel 5. Typically this change would occur after around 140 rotation of the wheel 5 and increases the velocity of the wheel to about 100/mum. Evidently the actual speeds achieved depend upon the power of the gas generator and the relative geometry of the teeth in a particular pretensioner, and this can of course be adapted to suit the situation and the performance required.

Figure 4 illustrates a slightly later position of the chain, continuing the high speed drive of the pinion wheel, and the more closely spaced inner teeth 7 of the wheel 5 are now fully engaged with the chain teeth 10.

In Figure 5, the end position of the sequence is shown with the chain 1 having been driven to the end of the channel 2 and the trailing end of the chain 1 disengaged from the pinion wheel 5. At this end position (in this example) the pinion wheel has been driven 970". The total length of chain in this example is 135 mm. If the chain 1 and the wheel 5 comprised only the low speed, widely spaced interlocking teeth, then, in this example, the total rotation would only amount to 6750. Hence it can clearly be seen that this arrangement provides a substantially improved pretensioner performance for the same length of chain.

More sections may be introduced in the chain to effect higher gearing ratios if more webbing rewind is required for the same length of chain and gas generator power.

Modifications to the arrangement are envisaged. The low-gearing chain links may be replaced by widely spaced teeth or other inter-engageable members. The chain may be replaced by a non-flexible rack although the flexible chain is preferred since it allows for a smaller package size. An embodiment using a rack is shown in Figure 9. The rack 28 has three sections 28a, b, c with progressively more closely spaced teeth. The sprocket 5 has three sets of gear teeth 7a, b and c to engage respective sets of the rack teeth 28a, b, c.

Some alternatives are shown in Figures 9 to 13 where the driving chain 1 is dividable into smaller sections after it passes the sprocket 5. This has the advantage of allowing for a more compact receiving chamber 17 for the expended chain.

Figures 9 and 10 show, in cross section, an embodiment of the invention in which the chain is formed of a cable or line 18 linking a string of abutting balls 19. The sprocket teeth 7 take the form of pointed sharp blades which fit between the balls 19 and cut into the joining cable 18 to divide the balls 19 one from each other. Figure 9 shows the rest position for this embodiment. Figure 10 illustrates the operating position. The chain 1 is separated by the blade like teeth 7 and the individual balls 19 fall into the receiving chamber 17.

Figure 11 illustrates another embodiment in which the chain 1 is formed of a series of interlinked elements in the form of hooks 20. Each element has a peg 21 at one end and an open arc or hook 22 at the other end to link with the peg of the adjacent element. The elements 20 may be relatively loosely linked and held together only by the restricted height A of the guide channel 2 on the entry side of the sprocket 5. Alternatively they could be constructed to clip together but with insufficient grip to withstand the separating forces imparted to them when they are driven at speed past the sprocket 5 and enter the receiving chamber 17 which is of unrestricting height B which is larger than that of the channel 2 and allows the elements to unhook from each other.

Figures 12a and b illustrate another embodiment in side view (Figure 12a) and top view (Figure 12b). The chain 1 takes the form of a frangible rack. The rack comprises a series of segments 22 held together by clips 23 in elongate chaining device 24. The chaining devices 24 fit on opposite sides of the segments and the clips 23 engage respective recess 25 in the segments 22.

As the chain 1 passes the sprocket 5 to gear teeth 7 on the sprocket 5 forces the segments 22 apart and un-clips them from the chaining devices 24.

Another alternative would be to use rollers to make a chain.

Figure 13 illustrates an embodiment in which the chain 1 is formed by balls 19 encapsulated in a foam tube or cylinder 26. The foam is cut into separates pieces 27 by teeth on the sprocket 5 and fall into receiving chamber 17.

This embodiment has additional advantages in that the foam reduces noise levels and assists sealing of the guide channel 2. An additional seal attaches the foam tube 26 to piston 16 to maximise the effect of gas pressure from the gas chamber 4 on the chain 1.

In each of the embodiments of 9 to 13 it is envisaged that gearing can be introduced, in a similar way to the embodiment of Figures 1 to 7. For example in different sections of the chain different forms of segments could be used in Figures 12, 12b or different dimensions of hook elements for the embodiment of Figure 11.

Claims

1. A pretensioner for a vehicle safety restraint retractor comprising a driving member, a pinion wheel connectable to a retractor spool for turning the spool to wind seat belt webbing thereon, and force generating means for moving the driving member in a path which passes the pinion wheel, to turn the wheel and consequently the spool, wherein the driving member and the pinion wheel have at least two sets of spaced interengagement members, the members of one of the sets being more closely spaced than the members of the other set.

2. A pretensioner according to claim 1 wherein the driving member is flexible.

3. A pretensioner according to claim 2 wherein the driving member comprises a flexible chain and the first set of interengagement members comprises radially extending teeth on the pinion wheel spaced to engage correspondingly spaced links in the chain.

4. A pretensioner according to claim 3 wherein the second set of inter-engagement members comprises additional radial teeth on the wheel, axially offset from the first set of teeth and more closely spaced.

5. A pretensioner according to claim 4 wherein the additional teeth are adapted to engage with a second set of correspondingly spaced links in the chain.

6. A pretensioner according to claim 4 wherein the additional teeth are adapted to engage with a second set of correspondingly spaced teeth on the chain, offset from the first set of links.

7. A pretensioner according to any one of the preceding claims wherein the force generating means comprises a gas generator.

8. A pretensioner according to claim 7 wherein a sealing plunger. is arranged at one end of the chain.

9. A pretensioner according to any of the preceding claims wherein the driving member is guided in a guide channel which tangentially passes the pinion wheel.

10. A pretensioner substantially as hereinbefore described with reference to figures 1 to 7, figure 8 or any of figures 9 to 13.