WO2009067053A1

WO2009067053A1 - Improvements in relating to a controlled release mechanism

Info

Publication number: WO2009067053A1
Application number: PCT/SE2007/050863
Authority: WO
Inventors: Erik Hjerpe
Original assignee: Autoliv Development Ab
Priority date: 2007-11-19
Filing date: 2007-11-19
Publication date: 2009-05-28

Abstract

Various arrangements are disclosed providing a mechanica! connection capable of controlled temporary weakening, for example when a pre-crash sensor is activated in a vehicle safety system, to ensure fracture of the connection if a crash actually ensues, but to avoid such fracture if no crash occurs. The connection may comprise a unitary component, such as a bolt or tube (10), or a composite assembly, but includes, in either case, a first part (10a), a second part (10b), and means (14) connecting the first and second parts, and a cavity or chamber (16) formed between the first and second parts. The cavity or chamber (160 is connected with a pyrotechnic gas generator designed to provide, when fired, a gas pressure in the cavity of a magnitude to apply temporarily a stress between the first and second parts which is in itself less than required to break the first part from the second but which does temporarily reduce the magnitude of the externally applied forces required to break the first part from the second.

Description

improvements in relating to a controlieci reiease mechanism

The present invention relates to a controlled release mechanism, for example to a controlled release mechanism for use in or forming part of an automotive safety device.

There are situations, particularly in relation to automotive safety devices, where it is desirable to have an element reiease preferentially in a pre-determined set of circumstances. For example, it is known to employ, in automobiles, so-called pre-crash sensors which, in response to stimuli frequently indicative of an impending crash, such as excessive deceleration, will release certain connections between components. GB2412094 discloses such an arrangement in which a connector has an interna! cavity and has a wall, surrounding the cavity, which is weakened at a iocation of preferred fracture and in which a pyrotechnic squib is fitted within the internal cavity. The squib, when fired by the triggering of a pre-crash sensor, causes the connector to fracture at the preferred location to reiease the item secured by the connector.

There are, however, circumstances in which a pre-crash sensor may be triggered and yet an actual crash does not ensue, for example as when emergency braking brings the vehicle concerned to a halt before the anticipated impact or when, for example, the vehicle manages to miss the vehicle or object with which a collision was anticipated. Sn such a situation, where the triggering of the pre-crash sensor is required to ensure that a mechanical connection of some kind in a vehicle will break in the event of the vehicle being involved in a crash, it would be desirable for the breaking of that mechanical connection to be avoided if a crash does not actually occur. The applicants have conciuded that in such a situation it would be desirable for such a mechanical connection to be weakened only temporarily, whilst there remains imminent danger of a crash. Thus, after a potential crash situation, in which the respective pre-crash sensor has been triggered, if no crash has actually occurred, the vehicle can still safely be driven, at least to an appropriate servicing facility.

It is an object of the present invention to provide an arrangement affording the possibility of a controlled temporary weakening of such a connection, rather than complete fracture of such a connection, in response to triggering of such a pre-crash sensor, leaving the actual crash, if it occurs, to effect compiete fracture, (or in response to triggering of an in- crash sensor, leaving forces arising externally from the crash to effect compiete fracture, or not, depending upon the nature or severity of the crash).

According to the present invention there is provided an arrangement providing a mechanical connection capable of controlled temporary weakening, the connection comprising a first part, a second part, means connecting said first part with said second part and defining a first yield stress at which said first part and said second part will be separated or at least displaced relative to each other by externally applied forces, a cavity or chamber being provided between said first and second parts, the arrangement including a fluid pressure source capable of providing, on activation, a fluid pressure of predetermined value in said cavity of a magnitude to apply temporarily a stress between said first and second parts which is iess than said first yield stress, to temporariiy reduce the magnitude of the externally applied forces required to separate or cause such displacement between said first and second parts, and thereby temporariiy to reduce the effective yield strength of the connection,

in some arrangements according to the invention, said first and second parts comprises first and second elements in frictionai engagement with one another and capable of slipping reiative to one another under a force sufficient to overcome friction between said elements, said means connecting said first part with said second part comprising fastener means urging said elements against one another to generate a first reactive force between said elements defining a said first yield stress at which one said element will slip reiative to the other against the frictiona! force between the elements, said cavity being defined between said first element and said second element, whereby sad fluid pressure in said cavity will temporariiy reduce the reactive force between the elements and wilS thus reduce the magnitude of the externally applied force needed to cause one said element to slip relative to the other.

In other arrangements according to the invention, said first and second parts comprises first and second elements held together by fastener means which define said first yield point as the stress between said elements at which said fastener means will yield, allowing the first and second elements to be separated, said cavity being defined between said first eiement and said second element, whereby, when said predetermined fluid pressure is applied to said cavity, it will provide a force tending to separate the first and second elements whereby the force which needs to be applied externaϋy between said elements to cause said faster means to yield is reduced below said first yield stress whilst said pressure is applied.

in a further embodiment, said first and second parts comprises first and second portions of a unitary member and said connecting means comprises a further portion of said unitary member interposed between said first and second parts, said cavity being provided within said connecting means.

The unitary member may take the form of a bolt or bar, said cavity being provided at an intermediate position in said boit or bar and said connecting means comprising the part of the bolt or bar surrounding said cavity.

Alternatively said unitary member may take the form of a tube, said cavity being provided at an intermediate position along said tube and taking the form of a circumferential passage or gallery within the wail of said tube, and said connecting means comprising the part of the tube wall in which said passage or gallery is provided.

In preferred embodiments of the invention, the fluid pressure source comprises a pyrotechnic device provided externally of said chamber or cavity and connected therwith by an inlet passage, and an exhaust passage is provided for release of gas pressure from said chamber or cavity.

Embodiments of the invention are described before by way of example with reference to the accompanying drawings in which:-

Figure 1a is a schematic sectional view illustrating one arrangement embodying the invention,

Figure 2 is a view similar to Figure 1 a but illustrating yielding of the connection of Figure

Figure 3 illustrates an arrangement similar to Figure 1 without an arrangement in accordance with the present invention, Figure 4 is a schematic sectional view illustrating a variant arrangement,

Figure 5 and Figure 8 are schematic sectional views illustrating further embodiments of the invention,

Figures 7 and 8 illustrate a further embodiment of the invention, Figure 7 being a schematic sectional view and Figure 8 a plan view,

Figure 9 illustrates a variant of the arrangement of Figures 6 and 7, and

Figure 10 illustrates one application of the invention.

Referring to Figure 1 , this illustrates, schematically, in section, a tubular member 10 which is secured at one end to structure 12 which may be, for example, part of the vehicle chassis or the like, the tubular member 10 being designed to fracture at a location 14, between an upper part 10a of the member 10 and a lower part 10b, in an emergency situation, for example, where the structure shown forms part of an automobile, in a crash situation, as part of a driver or passenger safety arrangement. To provide for such fracture at the location 14, a circumferential cavity or gallery 16 extends within the wail 17 of the tubular member (10) at the location 14. An inlet passage 18 extends into the gallery 16 from the peripheral surface of the tubular member 10 and is connected, by an appropriate gas-tight connection, (not shown), with a pyrotechnic gas generator arrangement, known perse and not shown. A vent or exhaust outlet 20 communicates with the gallery 16 at a location remote from the inlet 18 and, in the arrangement shown, communicates with a outlet port on the exterior surface of the tubular member 10. It will be appreciated, of course, that the pyrotechnic gas generator might be located within the tubular member 10 and connected with the gallery 16 via an inlet passage extending from the inner surface of the tubular member to the gallery and that, likewise, the vent outlet 20 might open onto the internal surface of the tubular member. Referring to Figure 2, a bending force applied to the tubular member, or a tensile force applied thereto, will, if of sufficient magnitude, cause the tubular member 10 to fracture at the location 14 due to the reduction in effective cross section of the tubular member provided by the presence of the gallery 16. However, if the gallery 16 is pressurised by pressurised gas provided by activation of the pyrotechnic gas generator, the force, applied externally to the tubular member 10, required to fracture the member 10 at the location 14 will be correspondingly reduced, since at any particular location around the member 10 at the location 14, the net tensile force acting between the parts 10a and 10b of the tubular member above and below (as viewed in Figures 1 and 2) the gallery 16 will be equa! to the sum of the force due to the internal pressure within the gallery and the tensile force applied externally to the member 10. The pyrotechnic gas generator is so designed , taking account of the dimensions and material strength of the member 10 and of the dimensions and configuration of the gallery 16, that when the gas generator is fired, the internal pressure, within the galiery 16, of the gas generated is insufficient, alone, to fracture the member 10. Accordingly, if a crash does not then actually occur, the member 10 will remain intact and the pressurised gas within the chamber 16 will leak away relatively gradually through the vent outlet 20. Sn such a situation, it will merely be necessary to replace the pyrotechnic gas generator to restore the system, (e.g. a safety system in an automobile), to its origina! condition. Of course, an appropriate indicator wil! be provided within the vehicle to alert the driver, or a service mechanic, for example, to the fact that the pyrotechnic gas generator has been fired and requires to be replaced.

if, on the other hand, the sequence of events immediately following activation of the pyrotechnic gas generator does indeed include an actual impact or crash, then the additional force, resulting from the crash, applied to the member 10, in combination with the pressure within the chamber 16, will ensure that the member 10 will fracture at the location 14 if the stress to which the member 10 is subjected in the crash exceeds that at which it is designed to fail taking account of the assisting gas pressure within the gallery 16.

Referring to Figure 3, if the gallery 16 were not provided, then the member 10 would need to be locally weakened to a greater extent than in the case of the arrangement of Figures 1 and 2, with the result that in, for example, a near-accident situation involving high braking forces, or perhaps even under clumsy handling, the member 10 might fracture in a non-accident situation or might accidentally be bent or distorted, or the structure 12 to which it is secured might likewise be bent or distorted, even when this would not be necessary to secure the safety of the vehicle driver or passengers.

Figure 4 illustrates a variant of the arrangement of Figure 1 in which an otherwise solid bolt or bar 10' has a simple, e.g. a quasi-spherical, cavity 16' therein at a desired fracture location, the cavity again being connected by an inlet passage (not shown) to a pyrotechnic gas generator or the like and having an outlet or vent passage (not shown). The cavity 16' may be centred on the longitudinal axis of the bolt or bar, if fracture under tension is contemplated in an accident situation, or may be offset from such axis if partial fracture (on the side closest to the cavity) and bending (on the opposite side of the bolt or bar) is contemplated in an accident situation. Of course, a hollow or tubular member might similarly be provided with a cavity iocated on one side thereof or extending only partially around the wall of the tubular member, for fluid (e.g. gas) pressure-assisted failure in an accident situation in the same way as described above with reference to Figures 1 and 2.

Figure 5 illustrates an arrangement in which a bolt 10" having a localised internal cavity 16" connected via a passage 18" with a pyrotechnic gas generator (not shown), and further connected via a passage 20" with a vent outlet, is used to secure a first plate 30 and a second plate 32 together, in this arrangement, pressurization of the cavity 18" by activation of the pyrotechnic gas generator acts to assist fracture of the bolt 10" under forces either tending to move the first plate 30 away from the second plate 32 along the axis of the bolt or under axial tension in the bolt resulting from a sliding or shear dispiacement of one plate relative to the other, as illustrated by the arrows, but such pressurization is again insufficient in itself to fracture or permanently deform the bolt 10".

Referring to Figure 6, in another arrangement embodying the invention, a tube or pipe 36 has a flange 34 projecting outwards from the pipe and a cavity 16'" is defined between the flange 34 and the adjacent external pipe surface, on the one hand, and a dished annular member 38 on the other hand, the member 38 being welded or press- fitted to the pipe and engaging the flange 34. Again the cavity 16'" is connected, by an inlet passage (not shown) to a pyrotechnic gas generator (not shown), and is arranged to be pressurized, in a pre-crash situation, or analogous situation, by firing of the pyrotechnic gas generator, to a pressure which in itself is insufficient to break the flange 34 from the pipe, (or to break the pipe adjacent the flange), but which weakens the connection of the flange with the pipe in the sense that whilst the said pressure prevails, the external force required to pull the flange from the pipe 36 is less than would be the case in the absence of such pressure. Again the weakening is temporary since if no such external force is applied, the gas in the cavity 16"' rapidly disperses either through a dedicated exhaust/vent passage (not shown) or through spaces left by allowing the connection between components to be less than completely air-tight. That is to say, the characteristics of the pyrotechnic gas generator, the configuration and size of the cavity, etc., are once again designed so that a fracture of the pipe or flange or boit wiii not normally occur until a first externally applied yield stress is reached but wili occur at a significantly lower externally applied yield stress if the cavity 16'" is pressurized by activation of the gas generator.

Figures 7 and 8 exemplify a further arrangement in accordance with the invention in which a bracket 50, for example providing a pivotal connection for a shaft or arm 52, is secured to a first, piate 54 which Is clamped, by bolts 56, to a planar part 58 which may be, for example, part of the frame of a motor vehicle. The plate 54 has a substantially planar surface with which it engages a correspondingly pianar surface of the part 58. A gas inlet 60 is formed in the planar part 58 at a location substantially central with respect to the p!ate 54 and a pyrotechnic gas generator 62 is secured to the part 58 on the side of part 58 remote from the plate 54, the gas generator having a gas outlet communicating directly with the gas inlet 60. if the gas generator 62 is activated by a pre-crash sensor, for example, the gas generator will produce a body of gas under pressure acting between the opposing surfaces of the plate 54 and the part 58 which wil! increase the tensϋe stress within the bolts 56. !f this tensile strength is increased further by forces arising in an actual crash situation, the bolts 56 can fracture in the intended manner, whilst if no actual crash occurs, the gas generated will leak away and the bracket 50 will remain attached to the part 58. In this case, of course, whilst no significant cavity may be readily discernible between the plate 54 and the part 58, because the cooperating surfaces of the plate 54 and the part 58 are not perfectly fiat and smooth, there does exist space, and hence a (flat) cavity between these surfaces into which pressurized gas can pass to urge the plate 54 and part 58 apart.

However, in the assembly illustrated in Figures 7 and 8, in which the arm 52 has its longitudinal axis substantially inclined with respect to the planes of the parts 54 and 58, the connection between the parts 54,58 is intended primarily to withstand shear forces parallel with the these planes, and the resistance to such shear displacement of the parts 54 and 58 relative to one another is dependent, at least initially, on the friction between the pianar parts 54,58. By tightening the bolts 56 a tightening force is achieved which determines the level of this friction in the assembly, if the adjacent surfaces of the parts 54,58 are subject to pressure of gas between these parts, then the shear force (determined by the friction) that the assembly can withstand is reduced and may be so reduced as to comprise only the shear strength of the bolts 56.

Figure 9 illustrates a variant, in which the region of the part 58 which opposes the plate 54 is recessed or domed as indicated to present a pre-formed cavity between the plate 54 and part 58, said cavity being located inwards of the bolts 56. Figure 9 also illustrates a vent passage 20'" although, in practice, such a vent passage may not be required if the surfaces of the plate 54 and the opposing plate 58 do not meet sufficiently accurately to form a gas tight seal.

It will be understood that, in an arrangement such as described with reference to Figure 5, in which the friction acting between superimposed plates is to be temporarily reduced in a pre-crash situation, a chamber or cavity similarly defined between the plates in the same manner as described with reference to Figures 7 and 8 may likewise be connected via an inlet passage with a pyrotechnic gas generator to urge the plates apart and thus reduce the friction therebetween temporarily, when such gas generator is fired.

Figure 10 illustrates, in a motor vehicle context, an arrangement embodying the invention in which link arms 90 connecting the front wheel axles of a vehicle are secured to a sub-frame 94 by connection arrangements in accordance with the invention, for example of the form described with respect to Figures 7 to 9, so that in the event of a frontal impact, the front Sink arms 90 may be broken away from the sub-frame and the front wheels 92 may be displaced to the side as indicated by broken lines, to minimise the risk of the wheels intruding into the passenger compartment or cabin. Likewise, the connections between sub-frame 94 and a cabin floor of the vehicle may be effected by connection arrangements in accordance with the invention so that such connections will break in the event of an accident or frontal impact, to prevent intrusion of the sub frame into the passenger space. Once more of course, the connections concerned are temporarily weakened but not broken by gas pressure produced by a pyrotechnic gas generator, or respective pyrotechnic gas generators, fired by a pre-crash sensors or sensors so that these connections will break readily under impact forces but will resume their normal strength upon dissipation of the gas pressure, if no impact occurs. Sn embodiments of the invention, the pyrotechnic gas generator can be designed to produce a desired maximum pressure, whereby, in effect, the pressure in the chamber or cavity can be tuned as desired for the application concerned. However, the selected pressure is only enough to reduce the strength of the connection or support, i.e. is always such as in itself to apply less than 100% of breaking stress to the connection or support.

A semi reversible system embodying the invention can be achieved if the material of the connection or support does not undergo plastic deformation, in order to avoid plastic deformation the pressure level inside the pressure chamber is iimited by appropriate design of the gas generator, for example by appropriate selection of the capacity of the

Sn some cases, however, for example in an arrangement according to Figures 7 to 9, the gas generator can be designed to produce such a high pressure within the pressure cavity or chamber that the material of the connection or parts thereof undergoes plastic deformation, even if an anticipated crash is avoided. Thus, in such a case, the maintenance work after a triggering of the gas generator which was not actually followed by a crash might involve no more than for example, replacement of the bolts 56 and the gas generator 62 in the arrangement of Figures 7 to 9.

ilst, in the embodiments described, the gas generator is Socated outside the pressure chamber or cavity (16, 18' ,16 ",16"'), and is connected with the pressure chamber by an inlet passage, it is of course possible depending upon the design of the structure providing the pressure chamber, for the gas generator to be accommodated within the pressure chamber or cavity.

When used in this specification and cSaims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. An arrangement providing a mechanica! connection capable of controlled temporary weakening, the connection comprising a first part (10a, 54), a second part (10b, 58), means (14,58), connecting said first part with said second part and defining a first yield stress at which said first part and said second part will be separated or at least displaced relative to each other by externally applied forces, a cavity or chamber (16, 16', 16", 16'") being provided between said first and second parts, the arrangement including a fluid pressure source (62) capable of providing, on activation, a fluid pressure of predetermined value in said cavity of a magnitude to apply temporarily a stress between said first and second parts which is less than said first yield stress, to temporarily reduce the magnitude of the externally applied forces required to separate or cause such displacement between said first and second parts, and thereby temporarily to reduce the effective yield strength of the connection.

2. An arrangement according to Claim 1 in which said first and second parts comprises first (30) and second (32) elements in frictiona! engagement with one another and capable of slipping relative to one another under a force sufficient to overcome friction between said elements, said means connecting said first part with said second part comprising fastener means (10") urging said elements against one another to generate a first reactive force between said elements defining a said first yield stress at which one said element will slip relative to the other against the frictional force between the elements, said fastener means incorporating said chamber or cavity defined between parts thereof acting between said first element (30) and said second element (32), or said chamber or cavity being defined directly between said first element (30) and said second element (32), whereby said fluid pressure in said cavity will temporarily reduce the reactive force between the elements and will thus reduce the magnitude of the externally applied force needed to cause one said element to slip relative to the other.

3. An arrangement according to Claim 1 in which said first and second parts comprises first and second elements (54,58) held together by fastener means (56) which define said first yield stress as the stress between said elements at which said fastener means will yield, allowing the first and second elements to be separated, said cavity being defined between said first element (54) and said second eiement (58), whereby, when said pre-determined fluid pressure is applied to said cavity, it wii! provide a force tending to separate the first and second eiements whereby the force which needs to be applied externally between said elements (54,58) to cause said faster means (56) to yield is reduced below said first yield stress whilst said pressure is ap

4. An arrangement according to Claim 1 in which said first and second parts comprises first (10a) and second (10b) portions of a unitary member (10) and said connecting means comprises a further portion (14) of said unitary member interposed between said first and second parts, said cavity (16) being provided within said connecting means.

5. An arrangement according to Claim 4 in which said unitary member takes the form of a bolt or bar (10'), said cavity (16') being provided at an intermediate position in said bolt or bar and said connecting means comprising the part of the bolt or bar surrounding said cavity.

6. An arrangement according to Claim 4 in which said unitary member takes the form of a tube (10), said cavity (16) being provided at an intermediate position along said tube and taking the form of a circumferential passage or galiery within the wall of said tube, and said connecting means comprising the part of the tube wall in which said passage or gallery (16) is provided,

7. An arrangement according to any preceding claim wherein said fluid pressure source is provided externally of said cavity (16) and is connected with said cavity or chamber by an iniet passage (18).

8. An arrangement according to any of Claims 1 to 6 wherein said fluid pressure source is provided within said chamber or cavity (16).

9. An arrangement according to any preceding ciaim wherein said fluid pressure source comprises a pyrotechnic device.

10 An arrangement according to any preceding claim in which an exhaust passage (20, 20', 20") is provided for release of gas pressure from said chamber.

11 An arrangement according to any preceding claim wherein said predetermined vai of said fluid pressure is in itseif insufficient to produce plastic deformation in said connection.

12. An arrangement according to any of Claims 1 to 10 wherein said predetermined vaiue of said fluid pressure is in itseif sufficient to produce plastic deformation in said connection but insufficient in itself to break said connection.