GB2351476A - Gas generator having an electromagnetic attenuator - Google Patents

Abstract

A vehicle safety arrangement comprises an active safety restraint, a gas generator (9) for providing a driving force to activate the safety restraint and a sensor (27) responsive to a vehicle emergency for detonating the gas generator (9). The gas generator (9) is electrically detonatable and electrical connecting wires (24) link the sensor (27) to the gas generator (9). At least one of the wires (24) is formed as an attenuator to inhibit accidental detonation of the gas generator (9) as a result of stray electro-magnetic waves.

Description

2351476

PRETENSIONER DESCRIPTION

The application is divided from application no. 99 10 500.9 and is related to co-pending divisional no. OOZi411.c#_ 5 simultaneously filed.

The present invention relates to a pretensioner for a vehicle occupant safety restraint and particularly to a buckle pretensioner.

Pretensioners are used to rapidly pull in any slack in a safety restraint seat belt at the onset of a crash condition so as to more securely restrain the occupant against forward movement and potential injury by collision with internal features of the vehicle. In addition, the pretensioning operation aims to pull the occupant into, or at least towards, the correct seating position so as to maximise the effect of a second restraint such as an airbag.

A modern seat belt is known as a 3-point restraint because it is secured to the vehicle at three points arranged about the occupant so as to provide a diagonal torso section and a horizontal lap portion to hold the occupant in the seat. The belt is attached to the vehicle by a spring loaded retractor tending to pull in the belt, and by a buckle for quick release of the belt.

Pretensioners can be sited at the retractor or at the buckle end of the restraining seat belt. The present invention relates particularly to a buckle end pretensioner and aims to provide an improved pretensioner.

2 According to the present invention there is provided a vehicle safety arrangement comprising a 3-point vehicle safety restraint airbag seat belt, a sensor responsive to a vehicle emergency, a pretensioner, connected at the buckle mounting point of the seat belt, for pulling in a length of seat belt webbing in response to the sensor detecting an emergency, wherein the pretensioner comprises a force reservoir, and a piston located within and for movement along a guide cylinder tube under the force of gas from a gas generator, wherein the gas generator is electrically detonatable and electrical connecting wires link the sensor to the gas generator and wherein at least one of these wires is formed as an attenuator to inhibit accidental detonation of the gas generator as a result of stray electro -magnetic waves.

Such an attenuator could also be incorporated in wiring for a detonator for an airbag.

According to a preferred embodiment of the invention the pretensioner further comprises return motion blocking means for preventing movement of the piston in the opposite direction to the pretensioning direction, the blocking means comprising a locking member mounted to the piston, having an edge engageable with grooves on the inside of the cylinder, the locking member being inclined to the line of movement of the piston and the edge being biased towards the inside wall of the cylinder by a leaf spring, the arrangement being such that the edge rides over the grooves as the piston passes in the pretensioning direction but so that the edge engages one 3 of the grooves and locks the piston against further movement in the opposite, return motion direction.

The grooves preferably have a saw-tooth profile so that the edge contacts the long sides of the teeth in the pretensioning direction and contacts the short sides in the opposite direction.

The blocking member may be an elliptically formed, generally planar member, advantageously formed as a piece of metal.

Such a return motion blocking means can thus be constructed as a subassembly which has considerable advantages in manufacture and allows for a smaller package size.

According to another embodiment of the invention the piston is connected by a cable to the buckle mounting point of the seat belt arrangement, wherein a load absorbing crushable tube is arranged around the cable between the cable to buckle connection point and the buckle mounting point, to absorb loads generated on the buckle at the end of a pretensioning stroke.

This reduces damage to the buckle head.

According to a further embodiment of the present invention the pretensioner comprises a housing tube joined to the pretensioner guide cylinder tube, in sealing arrangement, by providing a pre-formed, groove on a first 4 one of the tubes, placing the second of the tubes over the first tube to cover the groove, applying radial pressure in the region of the groove to displace a portion of the material of the second tube into the groove on the first 5 tube.

The radial pressure may be applied with a rotating roller or by other means. The tube having the groove is preferably die cast with the groove preformed therein.

This method can provide for a strong, well sealed joint at relatively low cost and with minimum corrosion problems.

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:

Figure 1 is a exploded perspective view of the buckle end of a safety restraint according to one embodiment of the invention.

Figure 2 is a cross sectional view of the safety restraint of figure 1.

Figure 3 is an exploded perspective view of the buckle end of a safety restraint according to a second embodiment of the invention.

Figure 4 is an exploded perspective view of the buckle end of a safety restraint according to a third embodiment of the invention.

Figure 5 is a cross sectional view of part of f igure 1 illustrating a different attachment method.

Figure 1 shows an exploded view of a first embodiment of the invention. A buckle head 1, which is arranged to receive a locking tongue from a 3point safety restraint seat belt, is attached via a collapsable bellows 2 to an outer cable guide which is fixedly attached to a load bearing part of the vehicle by a locking bolt 4. A pretensioner shown generally at 5 is used to rapidly retract to the buckle head 1 towards the outer cable guide 3 in the event of a crash. The pretensioner 5 comprises a cylinder tube 6 in which slides a piston 7. A cable 8, which in this case is- double stranded, connects the piston 7 to the buckle head 1. Movement of the piston 7 along the cylinder tube 6 pulls the cable and hence pulls the buckle head 1 down towards its mounting point.

The piston 7 is driven along the tube by the force of gas f rom a gas generator assembly 9. This is located in the cylinder tube 6 within a gas generator housing which comprises lower part 10 and upper part 11. Channels 12, formed by grooves in each of the upper and lower gas generator housings, accommodate the two strands of cable 8 as it passes from the piston 7 and out of the back of the cylinder tube 6.

of course, any of a variety of known gas generators may be used from compressed gas cylinder to hybrid inflators in 6 which gas is generated from chemical reactions.

The two stands of the cable 8 are crimped into a cable assembly 13 which is secured in the piston 7. An 0 ring 14 is located in a groove at the forward end of the piston 7 to provide a seal against the internal surface of the cylinder 6. The internal surface of the cylinder 6 also comprises a series of grooves or saw-teeth formations to engage with a return motion blocking means 15. This comprises a generally elliptical planar member 16 mounted in the piston 7 and biased by a leaf spring 17 so that its outer edge engages with the grooves or teeth on the inside surface of the cylinder 6. The edge of the ellipse 16, and the shape of the grooves or teeth, are so profiled that the edge of the ellipse moves smoothly past the grooves or teeth on the inside of cylinder 6 in the pretensioning direction (shown by arrow P), but jams into the grooves and blocks a return motion of the piston 7 in the opposite direction. The spring 17 is a leaf spring and the return motion blocking means 15 forms a sub-assembly for ease of manufacture. At the end of the cylinder 6 is a break tube 18 of standard construction, which slows down the piston at the end of the pretensioning stroke and prevents it emerging from the end of the cylinder 6 (which would of course be undesirable and indeed dangerous).

The cylinder 6 is attached to an inner cable guide which has a cast or moulded arcuate channel 20 running through it about a central ring 21. The ring 21 is optionally surrounded by a rotatable roller 22 to reduce the friction felt by the cable 8 as it passes through the 7 channel 20. The inner cable guide 19, is surrounded by the outer cable guide 3 and is attached to a load bearing part of the vehicle by bolt 4 which passes through a locking washer 23.

It will be seen that the load from the buckle head 1 is taken by the outer cable guide 3 and the load f rom the cylinder 6 is taken by the inner cable guide 19, as also is the load from the cable 8. This has advantages in strength and in package size.

The arrangement of the roller 22 is described in applicant's co-pending application 96 25 476.8.

The gas generator assembly 9 is connected by wires 24 to a crash sensor (see figure 2) which detects a sudden acceleration or deceleration of the vehicle, or detects an impact, indicative of an emergency situation in this embodiment these wires are welded to the gas generator assembly to provide a high quality strong joint with a high temperature and shock tolerance.

one of the wires is chosen to be a special product manufactured by the company Raychem, which acts as an integral attenuator for the gas generator, to prevent accidental firing due to stray electro-magnetic waves.

A release indicator 25 is attached to the buckle assembly between the bellows 2 and the outer cable guide 3.

A fixing release indicator 26 surrounds the release indicator in its mounting position.

8 Figure 2 is a cross sectional view of the embodiment of figure 1 and like parts, are denoted by like reference numerals.

Thus buckle head 1 is connected by bellows 2 and a release indicator fixing 26 to the outer cable guide 3 which is secured to the vehicle by bolt 4. The gas generator sub assembly 9 is located within gas generator housing 12 all of which is contained in cylinder tube 6. Locking ellipse 16 together with its biasing spring 17 is located at the rear end of piston 7. At the end of the cylinder 6 is a break tube 18 to slow the piston at the end of its stroke.

A crash sensor 27 is connected by wire 24 to the gas generator assembly 9. The wire 24 which preferably includes an attenuator wire, passes through the cable guide 3 into the cylinder 6.

Figure 3 shows a partially cut away and partially exploded view of a second embodiment of the invention. Again like reference numerals refer like parts, where appropriate.

Thus a buckle head assembly 1 is connected via a cable 8 and a cable guide bracket 30 to the piston 7. In the vicinity of the buckle head 1, the cable 8 is protected by an outer plastic sleeve 31 which surrounds a washer 32 and a damper 33 attached to the cable 8. The damper 33 is a crush tube, for example an aluminium sleeve with ferrules.

This absorbs some of the load at the end of the pretensioning stroke as the buckle is drawn towards the 9 cable bracket 30 and thus reduces the incidence of damage to the buckle head 1 in a pretensioning operation.

The cable bracket 30 is attached to a f ixed part of the vehicle by bolt 4 which fits through inner and outer sleeves of a rotating bobbin 34 and 35 which serves to reduce the friction on the cable as it is pulled back through the cable guide 30.

In this embodiment the gas generator 9 is located in a gas generator housing 12 which is arranged external of the cylinder 6 at an angle thereto. The gas generator housing 12 is formed of a cast or moulded part connected between the cable bracket 30 and the cylinder tube 6.

The piston is sealed against the inside surface of the cylinder by a seal 36 at one end and an 0-ring seal 37 towards the other end.

Return motion of the piston is prevented by locking ellipse member 16 biased by leaf spring 17 located in the piston 7.

Figure 4 is a partially cut away and partially exploded view of a third embodiment of the present invention. Again like parts are denoted by like reference numerals where appropriate.

Buckle head 1 is connected by cable 8 to piston 7. The 3 washer 32 and a damper 33, mounted on the cable 8 just below the buckle head 1, is protected by a plastic sleeve 31 and further by a bellows 2.

The cable passes through the piston 7 via cable guide bracket 30 which is covered by an outer bracket trim 40 and fixed to the vehicle by bolt 4. Friction between the cable 8 and the guide bracket 30 is reduced using inner and outer rotating bobbins 34 and 35 respectively in the cable bracket 30. Gas generator 9 is located in the externally arranged gas generator housing 12.

The piston 7 is sealed in the tube 6 by means of seal 36 and 0-ring seals 37. Return motion of the piston 7 is prevented by locking ellipse 16 biased by leaf spring 17. A use switch connector and cable assembly is shown at 41.

A screw 38 serves to connect the guide bracket 30 to the gas generator housing 12. The cylinder tube 6 may be screwed to fix it into the gas generator housing 12.

Alternatively the cylinder tube 6 may be attached to the housing by a form of rolled joint and this is illustrated in figure 5. A pre-cast groove 50 is formed around the periphery of the cylindrical part 51 of the gas generator housing to which the cylinder tube 6 is to be connected. This cylindrical part 51 is the cable guide inner, as illustrated in the embodiment of f igure 5.

The cylinder tube 6 is then placed over this and a pressure roller 52 applied in the region of the pre-formed groove and rotated around the cylinder tube 6 so as to W displace some of the material of the cylinder tube 6 into the pre- formed groove 50 and thus lock the cylinder tube I I onto the part 51 of the housing.

This attachment method provides sufficient strength to resist the tensile load exerted when the pretensioner fires as well as the compressive and torsional dynamic load. it also serves to seal the tube 6 to the housing. The joint is strong and is relatively free of corrosion problems.

Optionally an autopharitic plating may be used on the tube 6 so that the rolling operation can be carried out without any corrosion occurring.

Previously known joining methods often exposed unplated base material in the tube 6 and introduced a tendency to corrosion.

Each of the three embodiments described have various different features which are interchangeable with other features of the same embodiment or of the other embodiments.

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Claims (7)

1. A vehicle safety arrangement comprising:

an active safety restraint, a gas generator for providing a driving force to activate the safety restraint, a sensor responsive to a vehicle emergency for detonating the gas generator to activate the restraint wherein the gas generator is electrically detonatable and electrical connecting wires link the sensor to the gas generator and wherein at least one of these wires is formed as an attenuator to inhibit accidental detonation of the gas generator as a result of stray electro- magnetic waves.

2. A vehicle safety arrangement according to claim 1 wherein the active safety restraint comprises:

a pretensioner, connected at a buckle mounting point of a seat belt, f or pulling in a length of seat belt webbing in response to the sensor detecting an emergency, and the pretensioner comprises a piston located within and for movement along a guide cylinder under the force of gas from the gas generator,

3. A vehicle safety arrangement according to claim 2 comprising a vehicle safety restraint airbag, inflatable under the force of gas from the gas generator.

4. A vehicle safety arrangement according to any one of the preceding claims further comprising a pretensioner housing tube joined to a pretensioner cylinder tube, in 13 sealing arrangement, by providing a pre-formed, groove on a first one of the tubes, placing the second of the tubes over the first tube to cover the groove, applying radial pressure in the region of the groove to displace a portion of the material of the second tube into the groove on the first tube.

5. A vehicle safety arrangement according to claim 4 wherein the radial pressure is applied using a rotating roller.

6. A vehicle safety arrangement according to claim 4 or claim 5 wherein said first tube is die cast, and the groove is preformed therein.

7. A vehicle safety arrangement substantially as hereinbefore described with reference to Figures 1 and 2 or Figures 3 and 4 optically combined with Figure 5 of the accompanying drawings.

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