Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60R—VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
  • B60R22/00—Safety belts or body harnesses in vehicles
  • B60R22/34—Belt retractors, e.g. reels
  • B60R22/46—Reels with means to tension the belt in an emergency by forced winding up
  • B60R22/4628—Reels with means to tension the belt in an emergency by forced winding up characterised by fluid actuators, e.g. pyrotechnic gas generators
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B45/00—Compositions or products which are defined by structure or arrangement of component of product

Definitions

• the present invention relates to a motor vehicle safety device including a gas micro-generator that is pyrotechnically triggered, the gas generated by combustion of a charge contained in the micro-generator serving to move an element of said device, in particular to move it in translation.
• the device may consist in a safety belt pretensioner or in a safety belt buckle retractor.
• the gas that is generated moves a piston (or balls) in translation, thereby entraining over its stroke a cable connected to the safety belt or to the belt buckle.
• micro-generator should therefore be distinguished from generators in which the gas generated by combustion of the pyrotechnic charge inflates an airbag.
• US-A-5,804,758, US-A-6, 145, 876 and US-A-5, 970, 880 illustrate such a type of generator, for the inflation of an airbag.
• a first generation of micro-generators of the above- specified type was charged with powder or granules of a pyrotechnic composition in order to obtain very short operating times, i.e. of the order of 5 milliseconds (ms) to 7 ms (time measured with a micro-generator placed inside an enclosure referred to as a "bomb" having a inside volume equal to 10 cubic centimeters (cm 3 ) at ambient temperature) .
• a first improvement consisted in using nitrocelluloses in order to increase the speed of combustion and obtain greater thicknesses for burning.
• compositions are now being used less and less, in particular because of the high levels of carbon monoxide that are given off.
• the present trend is to using composite propellants that are less toxic, that are much better at withstanding aging tests, and that have high combustion speeds, while further improving system performance and ensuring stable costs.
• Performance is said to be improved when the safety device is put into position quickly and progressively (i.e. "quasi-instantaneous” triggering), and also when there is an improvement in maintaining the generated gas pressure over time so as to prolong the effect of the safety device as long as possible.
• the desired stroke is shown in dashed lines. This means that although it is indeed desired to obtain a maximum flow of gas in a very short time span, it is also desired to obtain subsequent variation that is more progressive over time. For reasons of clarity, the common portions of the two curves are shown as being superposed.
• Patent document WO—A—02/43990 describes a gas generator in which the pyrotechnic charge is cured and is cast into the receptacle that is to contain it. As a result, its outer peripheral surface is in contact with the receptacle.
• the charge is burned only from a longitudinal axial channel formed in the block.
• Such a technique of putting the charge into place by curing and casting is difficult to implement and is made even more complicated given the small amount of space available inside a micro-generator.
• Patent document WO—A—99/00275 describes a gas generator that makes use of a charge constituted by a wound-up strip of combustible material.
• a porous or perforated support material can be interposed between the different thicknesses of the winding, which material should in any event be capable of transmitting combustion to the strip of fuel.
• the charge may be constituted by a multitude of blades extending radially within a cylindrical shape (like the gills of a mushroom) , with other blades of porous or perforated material being interposed between them.
• porous or perforated material does not constitute the burnable charge proper. With such a structure, the useful area that can enter into combustion is very large, thereby leading to combustion that is fast, uniform, and regular.
• EP-A-I 275 566 relates to a dual rate generator. Its structure is so particular so that it cannot be used to move an element of a safety device.
• An object of the present invention is thus to solve those problems by providing a motor vehicle safety device which comprises a pyrotechnically-triggered gas micro- generator that provides combustion, and thus positioning, that are fast and progressive, while also improving maintenance of the generated gas pressure over time.
• the present invention provides a motor vehicle safety device including a pyrotechnically-triggered gas micro-generator, the gas generated by combustion of a charge contained in the micro-generator serving to move a moving element of said device, in particular in translation, the device being characterized by the facts that: said charge is constituted by an essentially cylindrical monolithic block; the peripheral surface of the block, i.e. the surface defined by its generator lines, is spaced apart from the receptacle in which it is contained; and
• the device includes spacer means for holding said block in position, at least in the radial direction.
• the device includes spacer means for holding said block in the longitudinal direction; said radial and longitudinal spacer means are the same means, i.e. the spacer means serve simultaneously to hold the block in position in both the radial direction and the longitudinal direction; said spacer means consist in an elastically deformable element such as a spring or a pad of elastomer material; said spacer means comprise abutment members carried by a wall for retaining said block;
• said wall is a support wall for said block; said wall is an element of the wall of said receptacle, being either fitted thereto or integral therewith; • at least one of the parameters of mass, of shape, and of chemical composition of said charge is selected in such a manner that the pressure of the gas in the chamber in contact with said element reaches its maximum value in a time range of 8 ms to 14 ms after initiation of the gas micro-generator, with this pressure remaining at not less than 80% of its maximum value for 15 ms to 20 ms after initiation; said block consists in a cylindrical mass perforated by a series of axially-directed cylindrical channels, said array of channels being organized in such a manner that at the end of combustion, the block is reduced to a set of small discrete rods or "combustion cores", e.g.
• the device constitutes a safety belt pretensioner, a retractor for retracting a safety belt buckle, a pedestrian safety system, or a pyrotechnic anchoring system for securing a safety belt.
• FIG. 2 is a highly diagrammatic view of a motor vehicle safety device in accordance with the invention.
• Figures 3 to 6 are section views on a longitudinal midplane of four embodiments of a gas micro-generator that is pyrotechnically triggered and that is fitted to the above-mentioned device;
• Figure 7 is a graph plotting curves that illustrate the stroke of a pretensioned (or of a pyrotechnic actuator, indeed the length of belt wound into a retractor) as a function of the load that is transmitted thereto, with the bottom curve in bold corresponding to a prior art device, while the top curve corresponds to a device in accordance with the invention; • Figure 8 gives pressure rise curves as a function of time within devices in accordance with the invention;
• Figure 9 is an end view of one possible embodiment of a propellant block integrated in the device.
• Figure 10 is a curve showing how the perimeter of the Figure 9 block varies as a function of burned area.
• FIG. 2 is a diagram showing a motor vehicle safety device in accordance with the present invention.
• a retractor for retracting a safety belt buckle which buckle is referenced B.
• the buckle is secured to a cable C having a major fraction of its length engaged in a hermetically-closed sheath 1 in the form of an elongate cylinder.
• the cable C is secured to a piston-forming part 10 which subdivides the sheath hermetically into two distinct chambers, namely a first chamber 11 beside the buckle B and a second chamber remote from the buckle B.
• the chamber 11 In a rest position, i.e. in the absence of any impact (situation shown in Figure 2), the chamber 11 presents a volume that is much smaller than that of the chamber 12.
• Means can be provided inside the chamber 12 tending to urge the piston towards the position that is shown in Figure 2. Such means could be constituted by a spring (not shown) .
• the chamber 11 of the device communicates with a gas micro-generator MG, which is itself connected to an impact detector D.
• Figures 3 to 6 show four possible embodiments of a micro-generator suitable for being fitted to the device of the present invention.
• the generator 2 is generally cylindrical in shape about an axis X-X'.
• ignitor support 20 which is constituted by a hollow metal cylinder centered on the axis X-X' .
• Two small coaxial walls 200 and 201 are provided on one side of the support.
• the first wall 200 is of small thickness and of considerable height. It is close to the axial opening 0 through which the support passes.
• a second wall 201 surrounds the first. It is thicker and not so high.
• an initiator 3 of conventional type having electrodes 30 that extend through the opening about an annular part 4 constituting a shunt ring.
• An 0-ring 5 is engaged between the body of the initiator 3 and the wall of opening O in the support, which wall forms a support surface and a longitudinal spacer for the wall.
• the top end of the wall 200 is folded down onto the initiator inwardly towards the axis X-X', so as to hold it longitudinally in position.
• the support 20 is covered by a receptacle or case 21.
• the longitudinal cylindrical wall is referenced 210 while its transverse closure wall is referenced 211.
• 211 presents a setback 212 in the form of a circular depression centered on the axis X-X', such that in this region the outer face has a zone of small thickness that makes it frangible.
• the receptacle 21 is fastened to the support 20 via a peripheral collar 213 which is presented by the free end of the wall 210. It constitutes an annular flange that is outwardly directed at an angle of 90°.
• the collar is engaged between the two low walls 200 and 201 of the support, with the wall 201 being folded down (crimped) onto the collar 213 in order to hold the receptacle 21 in place.
• a charge of pyrotechnic material 6 such as propellant is housed in the receptacle 21.
• It is constituted by an essentially cylindrical monolithic block, e.g. obtained by molding or by extrusion.
• the longitudinal axis of the block is parallel to the axis X-X' and its peripheral surface, i.e. the surface defined by its generator lines is spaced apart from the receptacle 21 in which it is contained, specifically it is spaced apart from the wall 210.
• the device has spacer means for holding the block in the radial direction.
• these spacer means comprise a helical spring 7.
• the spring surrounds part of the initiator 3, bearing against the top end of the low wall 200. As a result, it is centered on the axis X-X' .
• the block 6 rests on the spring which tends to press the block against the transverse end wall 211.
• the spring 7 serves to hold the block both in the longitudinal direction and in the radial direction (transversely) .
• the spring prevents it from moving longitudinally, by bringing it into abutment against the wall 211. Furthermore, due to friction, the block is also prevented from moving radially.
• the block 6 is thus completely prevented from moving, thereby making its peripheral surface fully accessible. It should be observed that the plane transverse face of the block that faces towards the spring 7 is also accessible, at least in those zones thereof that are not in direct contact with the spring. In another embodiment that is not shown here, the spring 7 could be replaced by some other elastically deformable element, such as a pad of elastomer material.
• the micro-generator does not have a spring.
• the block 6 is placed against a support wall or plate 8.
• this wall or plate can be made of molded plasties material, or out of metal.
• This plate presents a fine annular support washer 80 having a through central opening centered on the axis X- X f and referenced 81.
• the outside diameter of this washer is smaller than the inside diameter of the receptacle 21.
• Six tabs 82 extend from the periphery of the washer. These are small tongues that are angularly distributed in regular manner and that form an obtuse angle relative to the bottom surface of the washer 80.
• the distance between the free ends of two diametrically opposite tabs 82 is greater than the inside diameter of the receptacle 21.
• the tabs 82 are somewhat elastic, so it is possible to engage the plate 8 in the receptacle and to hold it in position by friction between the tabs 82 and the wall 210. This is the situation shown in Figure 4.
• the washer 80 carries a low annular wall 83 extending axially and centered on the axis X-X' going away from the tabs 82. It extends substantially from halfway between the opening 81 and the periphery of the washer.
• the block 6 is placed bearing against the washer 80 and is prevented from moving radially by the low wall 83.
• the block is prevented from moving longitudinally (because it is in abutment against the plate 8 and the wall 211) , and radially (because it is held captive by the low wall 83) .
• the low wall could be discontinuous, i.e. made up of a plurality of distinct portions distributed around a circle.
• FIG. 5 also makes use of a support plate 8, analogous to that described above, except that it does not include a low wall 83.
• the block 6 is prevented from moving radially by an abutment-forming annular part 9 whose outside shape is such as to be suitable for pressing closely against the transverse wall 211 of the receptacle 21, and also against the base of its longitudinal wall 210.
• the central orifice of the ring presents a setback 90 forming a shoulder, so that it is constituted by two portions of different diameters, namely a smaller- diameter first portion in contact with the wall 211, and a larger-diameter second portion 91 of diameter equal to that of the block 6 (ignoring clearance) .
• portion 92 of the opening is situated immediately facing the thin zone of the wall 211.
• the annular part 9 and the plate 8 serve to prevent the block 6 from moving both longitudinally and radially. And once more, its peripheral surface is accessible, as is a large fraction of its transverse face beside the plate 8.
• Figure 6 makes use of a plate 8 identical to that shown in the preceding figure. In this case, there are extra thicknesses of material 214 projecting from the inside face of the wall 210 of the receptacle.
• These extra thicknesses can constitute fine splines of longitudinally-extending material. There may be three of them, being regularly distributed angularly. They are of dimensions suitable for receiving said block 6, ignoring clearance.
• the initiator When the initiator is operated, it causes the charge to burn.
• said charge is constituted by an essentially cylindrical monolithic block; the peripheral surface of said block is spaced apart from the receptacle in which the block is contained; and
• the device includes means for holding said block in position, at least in the radial direction.
• the block 6 is constituted by a cylindrical mass perforated by a series of axially-directed cylindrical channels 60.
• This array of channels is distributed in such a manner that each channel (other than a peripheral channels) is surrounded by six adjacent channels that are angularly equidistant.
• the perimeter of the block is referenced PER.
• the fine lines L represent the shape of the block at different instants of combustion when combustion takes place in parallel layers .
• the array of channels 60 is organized in such a manner that at the end of combustion the block losses its monolithic characteristic and is then reduced to a set of small discrete rods or combustion cores T which correspond to the separation regions between said channels 60. These cores are approximately triangular in section.
• a curve plotting the area of the block as a function of burned thickness would have substantially the same appearance, as would a curve showing the rate at which gas is generated by such a block as a function of time.
• This curve shows that the profile rises progressively to a peak, and that combustion then tails off from an angle extending from the falling edge of the curve. This enables operating time to be lengthened by a few milliseconds.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Crystallography & Structural Chemistry (AREA)
• Organic Chemistry (AREA)
• Automotive Seat Belt Assembly (AREA)
• Air Bags (AREA)
• Feeding, Discharge, Calcimining, Fusing, And Gas-Generation Devices (AREA)

Priority Applications (2)

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Citations (5)

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• 2004
  • 2004-11-25 FR FR0412511A patent/FR2878210B1/fr active Active
• 2005
  • 2005-10-20 DE DE112005002942T patent/DE112005002942T5/de not_active Withdrawn
  • 2005-10-20 WO PCT/EP2005/055432 patent/WO2006056517A1/en active Application Filing
  • 2005-10-20 JP JP2007541898A patent/JP5006205B2/ja not_active Expired - Fee Related

Patent Citations (5)

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