WO1997043147A1

WO1997043147A1 - Pretensioner

Info

Publication number: WO1997043147A1
Application number: PCT/GB1997/001256
Authority: WO
Inventors: Brian Edward Aiston
Original assignee: Alliedsignal Limited
Priority date: 1996-05-10
Filing date: 1997-05-09
Publication date: 1997-11-20
Also published as: GB2312827B; GB9709465D0; GB9609822D0; GB2312827A

Abstract

A pretensioner (2) for a vehicle safety belt, comprises a gas generator (6), means for detonating the gas generator in a crash, power transmission means for transferring energy from detonation of the gas generator into rotation of a ring gear (18) which is mounted within and spaced from a clutch housing (13), at least two planetary gears (14) mounted within the ring gear, a sun gear (15) fixedly mounted to a retractor spool shaft for rotation therewith and engagement means operable on a predetermined arc of motion of the clutch housing (13), to engage and rotate the ring gear (18), and consequently the planetary and sun gears to rewind the retractor spool. The power transmission means may be either a piston, a cylinder arrangement, a loose slug or pellet, or a worm mounted to move tangentially to a worm wheel fixedly mounted to the clutch housing. Alternatively the power transmission means comprises radial teeth or fins of the ring gear and gas jet impinging on the teeth to rotate the ring gear. This pretensioner is more compact than known designs.

Description

PRETENSIONER DESCRIPTION

The present invention relates to a pretensioner for a vehicle safety belt .

Pretensioners are used to rapidly rewind the retractor of a safety belt system to pull in a length of belt to more securely restrain a vehicle occupant in a crash. In particular the rewinding operation takes up slack in the belt to reduce forward movement of the occupant and more correctly positions him in the seat particularly for maximum efficiency of an air bag.

However, known pretensioners are large and bulky.

It is an object of the present invention to provide a pretensioner of compact design.

According to the present invention there is provided apparatus for rewinding safety belt webbing onto a retractor in the event of a crash, the apparatus comprising a gas generator, means for detonating the gas generator in a crash, power transmission means for transferring energy from detonation of the gas generator into rotation of a ring gear which is mounted within and spaced from a clutch housing, at least two planetary gears mounted within the ring gear, a sun gear fixedly mounted to a retractor spool shaft for rotation therewith and engagement means operable on a predetermined arc of motion of the clutch housing to engage and rotate the ring gear and consequently the planetary and sun gears to rewind the retractor spool.

According to one embodiment the power transmission means is a cylinder in fluid communication with the gas generator, a piston mounted in the cylinder in a gas tight fit and arranged to be moved along the cylinder when gas flows into the cylinder from the gas generators, and a cable one end of which is connected to the piston, and one end of which is connected to the clutch housing.

According to a second embodiment, the power transmission means comprises a worm mounted to move tangentially to a worm wheel which is fixedly mounted to the clutch housing. The worm may be of self-cutting nylon material, such as nylon 66, into which cut the teeth on the outer periphery of the worm wheel. Sufficient friction is generated to turn the clutch housing and thus engage the gears.

According to a third embodiment the power transmission means comprises radially protruding circumferentially spaced members such as teeth or fins on the outer circumference of the ring gear and a gas jet directing spout channelling the gas from the gas generator towards the radially protruding members for rotating the ring gear when a crash occurs.

According to a fourth embodiment, the power transmission means comprises a hollow channel connected for receiving gas from the gas generator in a crash, a piston (e.g. a slug or pellet) held in the channel, arranged to be released and pushed along the channel in the event of a crash, an arm or stop fixedly mounted on a clutch housing in line of the slug, a clutch arrangement adapted to engage the ring gear to the clutch housing after rotation of the clutch housing by a predetermined arc of circle.

Preferably the clutch of the first and fourth embodiments comprises roller clutch elements mounted in recesses in the inner surface of the clutch housing which recesses have an arcuate outer edge so that turning the clutch housing moves the roller elements radially inwardly to engage the ring gear. Preferably the roller elements are held in these recesses away from the ring gear under normal safety belt operating conditions. They may be held by plastic shims or by a multi-legged plastic spider member, the legs of which extend to and support the roller elements . They are released due to the resiliency of the shims or spider. The spider may also be used to hold the planetary gears .

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:

Fig. 1 is a cross-sectional view of a safety belt retractor with a pretensioner according to one embodiment of the invention;

Fig. 2 is a cross-sectional side view of the pretensioner of Fig. 1. Fig. 3 is a schematic side view of a pretensioner according to a second embodiment of the invention.

Fig. 4 is a schematic cross-section of the pretensioner of Fig. 3.

Fig. 5 is a sketch perspective exploded view of the pretensioner of Figs. 3 and 4.

Fig. 6 is a sketch exploded view of a pretensioner of a third embodiment of the invention.

Fig. 7 is a sketch exploded view of a pretensioner according to a fourth embodiment of the invention.

Fig. 1 is a side cross-sectional view of a vehicle safety belt retractor fitted with a pretensioner according to the present invention. Shown in the Figure is the rewind spring side of the retractor. The retractor is indicated generally at 1 and the pretensioner 2 is mounted on top of retractor housing 3. A rewind spring 4 (shown in part) is connected to axis 5 of a retractor spool onto which seat belt webbing is wound.

The pretensioner 2 comprises a gas generator 6 mounted in one recess of a pretensioner housing 7. The gas generator is connected via a channel 8 to an adjacent cylinder 9 in which a piston 10 sealing slides. The piston 10 is cast onto a cable 11. The other end of cable 11 is corrected via a crimped nipple 12 to a clutch housing 13, so that when the piston 10 moves up the pressure tube 9, the force exerted on the cable will rotate the clutch housing 13. Three planetary gears 14 are indicated by broken lines in Fig. 1 and will be described in further detail subsequently.

Fig. 2 is a cross-sectional front view of the side of the retractor shown in Fig. 1. Here it is clearly seen that the spool axis 5 abuts planetary gears 14 which in turn abut a sun gear 15. A retraction spring 4 is also connected to the axis 5.

In operation, when a crash occurs, a sensor is triggered, detonating the gas generator 6. Gas is released from the gas generator 6 and flows along channel 8 into the pressure cylinder 9. The gas pressure pushes piston 10 up the tube 9, pulling cable 11 and thus causing clutch housing 13 to rotate by approximately one third of a rotation. The rotation of the clutch housing, causes the clutch to engage the sun gear 15 (in a manner to be described hereafter) which in turn engages the planetary gears 14 and subsequently the spool shaft. By the use of a planetary gear system, a one third turn of the clutch housing is translated into many turns of the centre spool axis. Thus the length of the pressure tube 9 can be kept low providing a much more suitable package for fitting in a vehicle.

Fig. 3 illustrates an alternative way in which the gas from gas generator 6 causes the spool to rotate. The gas generator is mounted at one end of the retractor in such a position that, when activated, the release gas drives a worm

16 in a direction tangential to the centre spool shaft extension 17. The spool shaft extension 17 is provided with teeth on its outer periphery. The worm 16 is of self- cutting material such as nylon 66. As the worm 16 passes over the teeth of shaft extension 17, it engages them and causes the shaft and thus the webbing spool to rotate, in a rewinding direction. The position of the worm after the pretensioning stroke is shown at 16a.

Fig. 4 is a cross-sectional front view of Fig. 3 and like parts are denoted by like reference numerals. The worm 16 turns the shaft extension or worm wheel 17 which in turn turns the ring gear 18 and subsequently the planet gears 14 and the sun gear 15 attached to the shaft axis. The shaft axis 5 is preferably a keyed spindle. The retraction spring is shown at 4. The whole mechanism is covered by a mechanism cover 19.

Fig. 5 shows an exploded view of the embodiment of Figs. 3 and 4 and like parts are denoted by like reference numerals. It will be clearly seen from this view that as the worm 16, driven by gas from gas generator 16, moves in the direction of arrow A, it engages the worm wheel 17 to rotate it and the ring gear 18 in a clockwise direction shown by arrow B. The worm wheel 17 has a shoulder 20. Rotation of the ring gear 18 causes the planet gears 14 to rotate, also clockwise in the direction of arrow C. Sun gear 15 is thus moved in an anti-clockwise direction and causes the spindle of the webbing spool to rotate in an anti-clockwise direction as indicated by arrow D.

Fig. 6 shows an alternative embodiment. Gas generator 6 is mounted on the retractor housing with a bent outlet 21 which is directed at fins 22 of a ring gear 18. Preferably the gas in the gas generator is chosen so that it is semi- liquid on emission from outlet 21. Rotation of ring gear 18, which in the embodiment shown will be in a generally clockwise direction, causes planet gears 14 to rotate and subsequently sun gear 15 and spindle 5. The tooth profile and number within the ring gear 18 is chosen to give optimum performance depending upon the power of the gas generator and the torque required to turn the retractor spool. The gas generator is mounted in a gas generator housing which is attached to the retractor frame (not shown) . A mechanism bush ring 23 supports the planetary gears 14 on spindle 24.

Fig. 7 illustrates yet another alternative. Gas generator 6 is housed within a retractor outer case and its actual position is indicated by the broken lines 25. A channel 26 connects the outlet of the gas generator 6 to a plug or arm 27 mounted on a clutch housing 13. A slug (not shown) is held in channel 26 as a sealed unit. On detonation the gas from the gas generator drives the slug through the channel and pushes against the plug 27 thereby moving the clutch housing by at least one third of a revolution.

Mounted in recesses 28 of the clutch housing 13 are clutch rollers 29. These clutch rollers 29 are held in place by inner and outer shims (not shown) . The rollers are splined in a suitable configuration to match the splines as shown on the outside of ring gear 18. Under normal conditions (i.e. non-crash conditions) the clutch rollers are retained within the profile of the clutch housing by the inner and outer shims are kept clear of the ring gear 18. Under crash conditions however the clutch housing 13 is rotated and the clutch rollers are driven by the surface of their respective recesses, radially inwardly to mesh with the splines on the outside of ring gear 18. Teeth on the inside of ring gear 18 engage teeth on the planetary gears 14 and thus cause these to rotate, which in turn rotates the sun gear 15 and the spool spindle 5, thus retracting the seat belt webbing as required.

Claims

1. Apparatus for rewinding safety belt webbing onto a retractor in the event of a crash, the apparatus comprising a gas generator, means for detonating the gas generator in a crash, power transmission means for transferring energy from detonation of the gas generator into rotation of a ring gear which is mounted within and spaced from a clutch housing, at least two planetary gears mounted within the ring gear, a sun gear fixedly mounted to a retractor spool shaft for rotation therewith and engagement means operable on a predetermined arc of motion of the clutch housing to engage and rotate the ring gear and consequently the planetary and sun gears to rewind the retractor spool.

2. Apparatus according to claim 1 wherein the power transmission means is a cylinder in fluid communication with the gas generator, the apparatus further comprising a piston mounted in the cylinder in a gas tight fit and arranged to be moved along the cylinder when gas flows into the cylinder from the gas generators, and a cable one end of which is connected to the piston, and one end of which is connected to the clutch housing.

3. Apparatus according to claim 1 wherein the power transmission means comprises a worm mounted to move tangentially to a worm wheel which is fixedly mounted to the clutch housing.

4. Apparatus according to claim 3 wherein the worm is made of self-cutting nylon material,

5. Apparatus according to claim 3 wherein the worm is made of nylon 66

6. Apparatus according to claim 1 wherein the power transmission means comprises radially protruding circumferentially spaced members on the outer circumference of the ring gear and a gas jet directing spout for channelling gas from the gas generator towards the radially protruding members for rotating the ring gear in the event of a crash.

7. Apparatus according to claim 1 wherein the power transmission means comprises a hollow channel connected for receiving gas from the gas generator in the event of a crash, a piston in the channel arranged to be released and pushed along the channel by the gas in a crash, an arm or stop fixedly mounted on a clutch housing in line of the slug, a clutch arrangement adapted to engage the ring gear to the clutch housing after rotation of the clutch housing by a predetermined arc of circle.

8. Apparatus according to claim 2 or claim 7 wherein the clutch comprises roller clutch elements mounted in recesses in the inner surface of the clutch housing which recesses have an arcuate outer edge so that turning the clutch housing moves the roller elements radially inwardly o engage the ring gear.

9. Apparatus according to claim 8 comprising means for holding the roller elements in the recesses away from the ring gear under normal safety belt operating conditions.

10. Apparatus according to claim 9 wherein the holding means comprises at least one resilient plastic shim or by a spider member and released due to the resiliency of the shim or spider.

11. Apparatus according to claim 9 wherein the holding means comprises a resilient member with a plurality of legs extending toward and supporting in position the roller elements .

12. Apparatus according to claim 11 wherein the holding member is additionally arranged to hold the planetary gears .