GB2432407A

GB2432407A - Reusable safety device for a vehicle

Info

Publication number: GB2432407A
Application number: GB0523536A
Authority: GB
Inventors: Michel Kozyreff; Roger Darraba
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 2005-11-18
Filing date: 2005-11-18
Publication date: 2007-05-23
Anticipated expiration: 2025-11-18
Also published as: GB0523536D0; GB2432407B

Abstract

A safety device such as a hood or bonnet lifter is disclosed for a vehicle comprising a piston and cylinder arrangement 2,3,Fig 1. The piston and cylinder arrangement 2,3, Fig 1 is actuated by at least two individually ignitable pyrotechnic charges 12 for producing gas to drive the arrangement 2,3. The first charge (126, Fig,16) is ignitable to cause an initial cycle of operation of the safety device, and the second charge (127,Fig16) is actuable to cause a second cycle of operation of the device. A control unit (120,Fig16) produces an actuating signal to actuate one of the pyrotechnic charges in the event that the vehicle is involved in an accident situation. The device further incorporates an arrangement (130-133,Fig16) for initially enabling the first pyrotechnic charge (126,Fig16) to be actuated in response to an actuating signal, and for successively enabling the other pyrotechnic charge (127,Fig16) to be actuated upon receipt of a second actuating signal from the control unit (120,Fig16). The device is particularly suited such that it may be used more than once without requiring the replacement of any pyrotechnic charges by a skilled mechanic. The safety device may alternatively be a seat belt pretensioner.

Description

n 2432407

A SAFETY DEVICE

DescriDtion of Invention THE PRESENT INVENTION relates to a safety device, and more particularly relates to a safety device for use in a motor vehicle.

Many safety devices have been proposed for use in motor vehicles, being safety devices which are adapted to be actuated in response to an accident situation. Examples of such safety devices include safety-belt pretensioners and bonnet-lifters (hood-lifters), which are typically actuated by means of a pyrotechnic charge. The pyrotechnic charge generates gas which is used to move a piston to operate the safety device.

At the present time, whenever a device of this type has been actuated, it is necessary to replace the pyrotechnic charge before the safety device can be re-used. As some safety devices, such as hood- lifters and pretensioners, are actuated in response to sensors which sense a potential accident or impact, as opposed to being activated by means of an impact sensor, on occasions the safety devices are actuated when there is not an accident or impact.

Once the devices have been actuated it is necessary for the vehicle to be attended to by an appropriately qualified mechanic who will replace the pyrotechnic charges.

The present invention seeks to provide an improved safety device.

According to this invention there is provided a safety device, the safety device comprising an extendible gas driven arrangement which is actuated on operation of the safety device, at least two individually ignitable pyrotechnic charges for producing gas to drive the gas driven arrangement, a first charge being ignitable to cause an initial cycle of operation of the safety device, and n the second charge being actuable to cause a second cycle of operation of the device, there being a central control unit having an output providing an actuating signal each time the safety device is to be operated, the system comprising an arrangement for initially enabling a first pyrotechnic charge to be actuated in response to receipt of the actuating signal and for successively enabling the other pyrotechnic charge (or charges) for receiving the next actuating signal (or signals). The output may be a two-pole output.

In one embodiment the safety device is a bonnet-lifter (hood-lifter) for protecting pedestrians.

In an alternative embodiment the safety device is a belt tensioner.

In certain embodiments of the invention the gas driven device is a piston movable within a cylinder.

Preferably the cylinder is divided into first and second chambers by the piston, there being a gas flow path extending between the chambers, the gas flow path having a variable flow resistance.

Conveniently the piston is configured to change the flow resistance to the variable flow resistance path in response to the piston reaching a predetermined position when moving in a first direction.

Alternatively the extendible gas driven device is a telescopic tube having at least one fixed outer tube and at least one movable inner tube.

Conveniently the telescopic tube comprises two inner relatively movable tubes. n 3

A preferred device comprises a local control unit located adjacent to, and individually connected to the pyrotechnic charges, the local control unit enabling a specific pyrotechnic charge to be activated by the next actuating signal.

Conveniently the output of the central control unit is a two-pole output and the local control unit has a two-pole input connected to the output of the central control unit.

Preferably each pyrotechnic charge is associated with a respective squib resistor.

Conveniently the local control unit is configured to selectively close closeable switches which are connected respectively in series with respective squib resistors.

Preferably the central control unit is configured to generate diagnostic pulses with a low power relative to the actuating signal to diagnose the status of the squib resistors.

Advantageously the local control unit is configured to be powered by the diagnostic pulses.

Preferably each squib resistor is connected in series with a controllable switch between the two poles of the central control unit.

Conveniently the switches are controlled from the local control unit.

Preferably the local control unit is configured to sequentially close the switches associated with non-triggered squib resistors for a diagnostic cycle. 1 4

In an alternative form of the invention a plurality of squibs are provided each having a squib resistor, the squib resistors each being connected between two poles of a two-pole cable which received the actuating signal, successive squib resistors being associated with successively increasing resistive loads connected in series therewith.

In a further embodiment of the invention the central control unit is connected to a bus and provides coded signals to the bus, each pyrotechnic charge being associated with a respective decoder connected to the bus to decode signals from the central controller, the central controller being configured to generate a signal to initially enable a first pyrotechnic charge, so that the change may be actuated, and subsequently to generate a signal (or signals) to successively enable the other pyrotechnic charge (or charges).

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: FIGURE 1 is a diagrammatic sectional view of a safety device in the form of a bonnet-lifter (hood-lifter) showing the components of the safety device in an initial condition, FIGURE 2 illustrates part of the device of Figure 1 showing the components during an initial stage of operation of the safety device, FIGURE 3 is a figure corresponding to Figure 2 showing the components of the device at a further stage during operation, FIGURE 4 is a view corresponding to Figure 3 showing the components of the device at a further stage during operation of the device, fl FIGURE 5 is a view corresponding to Figure 4 showing the components of the device at yet a further stage in the operation of the device, FIGURE 6 is an enlarged view of part of the piston assembly that constitutes part of the device showing components of the piston assembly in a first position, FIGURE 7 is a view corresponding to Figure 6 showing components of the piston assembly in a second position, FIGURE 8 is a perspective view of a sleeve valve member forming part of the piston assembly, FIGURE 9 is a further perspective view of the sleeve valve member, FIGURE 10 is a sectional view of an alternative embodiment of a bonnet-lifter (hood-lifter) showing components of the device in a first condition, FIGURE 11 is a view corresponding to Figure 10 showing components of the device in a second condition, FIGURE 12 is a view of a safety device in the form of a safety-belt pretensioner, FIGURE 13 is a part circuit diagram and part block diagram illustrating one embodiment of the invention, FIGURE 14 is a block diagram provided for purposes of explanation, in FIGURE 15 is a circuit diagram provided for purposes of explanation, and FIGURE 16 is a further block diagram provided for purposes of explanation.

Referring initially to Figure 1, a safety device in the form of a hood or bonnet-lifter comprises a lower housing 1. Extending upwardly from the lower housing 1 is a cylinder 2 and contained within the cylinder 2 is a piston assembly 3. Part of the piston rod 4 of the piston assembly 3 extends above the cylinder 2 to engage part of a hood or bonnet 5. As will be described, upon actuation of the device, the piston is driven upwardly through the cylinder 2, thus causing the hood or bonnet 5 to be raised.

The housing 1 is of cylindrical form, having a cylindrical side-wall 6, closed at its lower end by a base 7 and having an upper wall 8. The upper wall 8 carries a circular upwardly directed flange 9 which surrounds an aperture 10 which is formed in the upper wall 8 (see Figure 2).

The interior of the housing 1 is divided into a plurality of chambers. In the described embodiment the interior of the housing is divided into two chambers by a central partition 10 which extends upwardly from the base 7. The partition 10 extends towards the aperture 10, but terminates a short distance from the aperture 10. The first chamber 11 contains a pyrotechnic material 12 which is retained in place by an upper retainer wall 13 which extends from the wall 6 of the housing 1 to the partition 10, the retainer wall 13 defining an aperture 14 therein, the aperture 14 initially being sealed by means of a rupturable foil 15.

Within the chamber 11, mounted on the base 7 of the housing, is a pyrotechnic squib 16, the pyrotechnic squib 16 containing a squib resistor 17. n

At this stage it is to be understood that if an appropriate electric signal is passed through the squib resistor 17, heat will be generated, thus igniting the squib 16 and the ignited squib 16 will ignite the pyrotechnic material 12 thus generating hot gas, which will rupture the foil 11, and flow into the upper part of the housing 1 to act on the piston assembly 3 to drive the piston upwardly.

It is to be appreciated that the second chamber 18, which is located on the far side of the partition from the chamber 11, contains a similar pyrotechnic material and igniting squib.

The lower-most end of the cylinder 2 is received as a sealing fit within the upstanding flange 9 provided on the upper wall 8 of the housing 1. The upper end of the cylinder 2 is inwardly swaged 19, the inward swaging carrying a sealing ring 20, the sealing ring 20 effecting a sliding sealing fit against the main part of the piston rod 4. The cylinder 2 is provided with an internal collar 21 provided adjacent the inwardly swaged region 19. The collar 21 serves to reduce the interior diameter of the cylinder 2 for a purpose that will

become clear during the following description.

The piston assembly 3 comprises the piston rod 4, which, as has been mentioned, extends upwardly beyond the end of the cylinder 2 to engage with the hood (or bonnet) 5. The lower end of the piston rod 4 carries a piston head assembly which is shown in greater detail in Figures 6 to 9.

The lower-most end of the piston rod 4 is provided with an axially extending internal blind bore 22. The blind bore receives and retains a mounting peg 23 which is formed on a piston head element 24. The peg 23 extends upwardly from the main body of the piston head element 24, the main body having a region 25 of a first uniform diameter, which is greater than the diameter of the peg 23, adjacent the base of the peg, and, beneath the region 25, a second region 26 of diverging form, in which the diameter of the body gradually increases. Formed within the body of the piston head element 24 is a gas flow passage, the gas flow passage comprising an axially upwardly extending portion 27 which extends upwardly from the base of the increasing diameter portion 26 of the piston head element 24, and a transverse bore 28 which emerges from the side-wall of the body in the region 25 of uniform diameter.

A flat washer-like stop element 29 is provided which is received on the mounting peg 23, and which rests on the shoulder that is created between the mounting peg 23 and the body portion 25 of uniform diameter, the stop member 29 being trapped between the lower-most end of the piston rod 4 and the piston head element 24. The stop element 29 protrudes radially outwardly beyond the piston rod 4. The stop element 29 is dimensioned to be received within the collar 21 provided at the top of the cylinder 2.

Slidably mounted on the piston head element 24 is a sleeve valve member 30.

The sleeve valve member has a cylindrical body portion 31 which has a uniform exterior diameter. Formed in the outer wall of the body is an encircling groove 32 and received within the groove 32 is a resilient "0"-ring 33 which acts as a sealing ring to seal against the interior wall of the cylinder 2 with a sealing sliding fit.

An axial bore 34 extends through the body 31. The bore 34 has an initial upper portion 35 of uniform diameter and a lower portion of diverging form, thus having an increasing diameter. As will become clear, the form of the portion of the bore of increasing diameter, 36, corresponds with the form of the portion 26 of the piston head element of increasing diameter.

Extending from the lower-most part of the body 31 are four arcuate fingers 37 which are equi-spaced about the bore 34, the inner surfaces being contiguous with the bore, the fingers 37 being spaced apart by gaps 38. The fingers do n not extend outwardly as far as the outer wall of the body. The fingers 37 may be resilient.

Formed in the flat upper face 39 of the body 31 are four radially directed slots 40 which each extend from the bore 34 to the outer periphery of the cylindrical body 31.

When the safety device is in an initial condition, the sleeve valve member 30 is mounted on the piston head element 24. The flat upper surface 39 is in engagement with the under-surface of the washer-like stop 29. The fingers 37 resiliently or frictionally grip the lower-most part of the piston head element 24 to retain the sleeve valve member 30 in the initial position. As can be seen from Figure 6, when the sleeve valve member is in the described position, two gas flow paths exist from the underside of the piston head assembly to the upper side of the piston head assembly. The first gas flow path is through the gaps 38 between the fingers 37, up between the spaced-apart portions of the sleeve valve member and the piston head element 24 which are of increasing diameter, that is to say the portion 36 of the sleeve valve member 30 and the portion 26 of the piston head element 24 and then radially outwardly through the four radially directed slots or channels 40. The second gas flow path extends through the axial bore 27 provided in the piston head element 24 and the radial gas flow passage 28, the gas flow path then again extending through the radially outwardly directed slots or channels 40. The first gas flow path has a larger effective cross-section than the second gas flow path, and thus the rate of flow of gas through the first gas flow path will be greater than the flow of gas through the second gas flow path.

Initially the piston is located at the lower-most part of the cylinder 2, with the lower-most part of the piston head element 24 and the fingers 37 of the sleeve valve member 30 being received within the aperture 10 formed in the upper wall 8 of the housing 1. n

When the safety device is to be operated an electric current is passed through the squib resistor 17 of the squib 16 present in the first chamber 11. The pyrotechnic material 12 is ignited and the foil 15 ruptures. Gas flows through the aperture 14, and fills the upper part of the housing 1, thus applying gas pressure to the under-surface of the piston head element 24. The partition 10 acts to direct the flow of gas upwardly, and minimises the risk that the hot gas will ignite the pyrotechnic charge in the second chamber 18.

The pressurised gas causes the piston head element to start moving upwardly, thus moving the piston rod 4 upwardly and thus moving part of the bonnet (or hood) 5 upwardly. As the piston moves upwardly (see Figure 2) gas from the pyrotechnic charge will fill the lower region 41 within the cylinder 2 beneath the piston head assembly, and that will tend to drive the piston upwardly. Some gas, however, will flow through the two described gas paths into the upper region 42 within the cylinder 2 above the piston head assembly. The gas cannot escape from this region because of the seal 20 provided at the upper part of the cylinder.

In the initial stage of operation of the safety device the gas pressure P1 within the lower region 41 is greater than the gas pressure P2 within the upper region 42 and thus, even as the piston is moving upwardly, the gas will tend to flow from the lower region 41 to the upper region 42. The force applied to the piston by the gas in the region 41 is effectively P1 A1, where P1 is the gas pressure within the region 41 and Al is the total effective area of the piston head assembly acted on by the gas. On the other hand, the force applied to the piston head assembly by the gas within the region 42 is P2*A2 wherein P2 is the gas pressure within the region 42 and A2 is the effective area of the piston head assembly acted on by the gas in the region 42. The effective area A2 is, of course, less than the effective area Al by virtue of the presence of the piston rod 4 within the upper region 42.

Whenever P1 *Al is greater than P2*A2 taken together with the resistance from the hood, the piston is accelerated upwardly.

As the piston begins to reach the termination of its upward stroke, the pressure P2 within the region 42 will increase. When P2, the pressure within the region 42 exceeds the pressure P1 within the region 41, gas will begin to flow from the upper region 42 to the lower region 41. As the piston continues to move gas in the upper region 42 it will become more compressed and a situation will obtain in which P2.A2 is greater than P1.Al (if the hood resistance is ignored), and thus the effective force applied to the piston head assembly by the gas in the upper region 42 will be greater than the force applied by the gas in the lower region 41, and consequently upward movement of the piston will then begin to be retarded. This provides an ideal operating characteristic for a safety device such as a bonnet (or hood) lifter as presently being described.

As the piston approaches the very end of its stroke, as shown in Figure 4, initially the upper surface 39 of the sleeve valve member 30 is engaged by an abutment formed by the lower end of the collar 21 provided at the top of the cylinder 2. The sleeve valve member 30 is thus prevented from moving upwardly, whilst the piston head element 24 continues to move upwardly. The annular washer-like stop element 29 enters into the collar 21 and then engages the under-surface of the seal 20 carried by the inwardly swaged region 19 of the cylinder 2. If the fingers 37 carried by the sleeve valve member 30 are resilient they may flex outwardly slightly as the sleeve valve member effectively moves downwardly relative to the piston head element 24 so that the sleeve valve member then has the condition illustrated in Figure 7 n in which the two portions of increasing diameter (that is to say the portion 36 of increasing diameter of the sleeve valve member and the portion 26 of increasing diameter of the piston head element 24) are in close abutment, thus effectively closing the first gas flow path which originally extended between these two regions. Thus, as can be seen in Figure 7, only one gas flow path, the second gas flow path, now remains open, that being the gas flow path through the axial bore 27 and the radial bore 28, which is a gas flow path dimensioned to allow only a relatively small flow of gas. Thus the gas flow path between the lower region 41 and the upper region 42 has the flow resistance thereof increased in response to the piston reaching the termination of its upward stroke.

The sleeve valve element 30 is retained frictionally in its new position.

If the hood of the motor vehicle is struck by a pedestrian, a substantial downward force may be applied to the piston rod 4 tending to drive the piston head assembly downwardly. As the piston head assembly moves downwardly gas pressure P1 in the region 41 will increase. This will cause gas to flow from the region 41 to the region 42 as shown in Figure 5 provided that P1, the pressure in the region 41 is greater than P2, the gas pressure in the region 42.

The gas will only flow through the single gas flow path constituted by the bores 27 and 28, thus giving a high degree of energy absorption, which is desired.

Regardless of whether the hood is or is not struck by a pedestrian, after operation of the safety device in the manner described, the hood may be re-closed, thus driving the piston assembly 3 back to the initial position as shown in Figure 1. As the piston head assembly is moved downwardly, initially the fingers 37 provided on the sleeve valve member will pass into the aperture 10, and the under-surface of the body 31 of the sleeve valve member 30, which is spaced radially outwardly from the fingers 37, will engage the upper plate 8 of the housing 1 in the region immediately surrounding the aperture 10. The sleeve valve member will thus be prevented from moving downwardly, whilst the piston rod 4 may move downwardly by a further limited extent, thus moving the piston head element 24 downwardly relative to the sleeve valve member until the under-surface of the annular washer-like stop element 29 comes into contact with the upper surface 39 of the body 31 of the sleeve valve member 30. The apparatus is now in the initial condition as illustrated in Figure 1, with the exception that the first pyrotechnic charge in chamber 11 has been ignited. However, it is to be appreciated that should a further accident situation or potential accident situation arise, the second pyrotechnic charge present in the chamber 18 may be ignited, when the above-described cycle of operation will be simply be repeated. Thus the device may effect repeated operations without receiving any attention from a skilled mechanic, and without replacing any pyrotechnic charges.

Whilst one type of safety device has been described with reference to Figures 1 to 9, Figures 10 and 11 illustrate a further form of bonnet or hood-lifter. In the arrangement shown in Figure 10 and 11, a lower housing 50 is provided, the lower housing containing a plurality of pyrotechnic elements 51, each of which contains a pyrotechnic material, a squib and a squib resistor to ignite the squib. Extending upwardly from the upper surface of the housing 50 is a first fixed tubular element 52. The tubular element 52 has, at its lower end, a radially outwardly directed flange 53 which is secured to the upper surface of the housing 50 and has, at its upper end, an inwardly swaged lip 54. Contained within the fixed tube 52 are two nested telescoping inner tubes 55, 56, the inner-most tube 56 having a closed upper end 57 which is engagement with the under-surface of a hood (or bonnet) 58.

As can be seen from Figure 11, upon operation of one of the pyrotechnic charges 51 gas is directed from the housing 50 into the spaced defined within the interior of the telescoped tubes 52, 55, 56, causing the tubes to become extended, thus raising the hood or bonnet. Following operation of the safety device, the device may be returned to its initial condition as shown in Figure 10, with the exception that one pyrotechnic charge has been ignited, and with the device in this form a second pyrotechnic charge may be ignited to cause the safety device to be operated. The pyrotechnic charges may be actuated successively to initiate successive cycles of operation of the safety device.

Figure 12 illustrates an alternative form of safety device which incorporates a housing 1, and a cylinder 2 of the form described with reference to Figure 1 which contains a piston assembly as described with reference to Figures 1 to 9. In this embodiment the piston rod 4 is connected a guide loop 60 through which part of a safety-belt 61 passes. It is to be understood that, upon actuation of the device, the piston rod 4 will extend from the cylinder 2, thus increasing the tension present in the safety-belt 61. The safety device is consequently operable as a safety-belt pretensioner.

In all of the re-usable safety devices described above, the safety device may be operated for at least a first time and at least a second time, without receiving detailed attention, although it is to be readily appreciated that the number of times that the device can be sequentially actuated depends upon the number of separate pyrotechnic charges and associated squibs which are provided. It is envisaged that design constraints will limit the number of pyrotechnic charges and associated squibs, but it is to be envisaged that in a typical practicable embodiment there may easily be between two and six separate pyrotechnic charge and associated squib units. It is desirable for the squib units to be ignited sequentially upon receipt of sequential signals from an appropriate accident sensor, with only one squib being actuated during any particular accident situation. fl 15

The embodiments of the invention are thus provided with a central control unit to provide an actuating signal and an arrangement for successively providing, in response to the actuating signal, successive triggering signals to successive squibs of successive pyrotechnic charges. Thus, successive squibs are successively enabled.

Referring, for example, to Figure 13, a sensor 70, (such as a sensor which senses a pedestrian located immediately in front of a vehicle when the vehicle is travelling towards the pedestrian at a speed in excess of a predetermined threshold) is provided which supplies an output to a central control unit 71.

The central control unit may be responsible for actuating various safety devices, but, it is sufficient for an understanding of the present arrangement to consider that the central control unit provides an actuating signal on a two-pole output line 72. The central control unit passes the signal to a local control unit 73. The local control unit 73 is located adjacent the safety device that is to be controlled. In the embodiment illustrated the local control unit 73 is connected to five separate pyrotechnic and squib units 74, each of these being equivalent, for example, to one of the pyrotechnic and squib units 51 of the embodiment of Figures 10 and 11. The local control unit 73 is configured to enable successive squibs so that the squibs are ignited in response to successive actuating signals.

Turning now to Figure 14, in one arrangement, a plurality of squib resistors 80, 81, 82, 83, 84 of respective squib and pyrotechnic material units, are each connected in series with a respective current controllable switch 85, 86, 87, 88, 89, between the two poles of the two-pole line 72. A further connection extends between the two poles of the two-pole line 72, this being a series connection comprising a diode 90 and a capacitor 91. Connected across the capacitor 91 are two input terminals of a logic unit 92. The logic unit 92 has outputs a, b, c, d aand e, each connected to a respective one of the current control switches 85, 86, 87, 88 and 89.

It is to be envisaged that the central control unit 71 will use low power diagnostic pulses to diagnose the status of the various squib resistors 80 to 84. Those low voltage pulses will charge the capacitor 91, thus providing a supply of power for the logic unit 92. The logic unit 92 may be controlled during a diagnostic cycle to selectively close selected switches 85 to 89 to enable the status of the associated squib resistors to be checked. However, the logic unit 92 will normally, after the diagnostic cycle is complete, retain one switch, such as the switch 85, in a closed condition, (which will enable the associated squib) until an actuating pulse is received along the two pole-line 72 which will cause ignition of the squib associated with the squib resistor 80. Subsequently the logic unit will ordinarily maintain the switch 86 in a closed condition until the squib associated with the squib resistor 80 is ignited, (thus enabling the next squib) and so on.

Figure 15 illustrates a further arrangement in which three squibresistors 101, 102, 103 are provided, each associated with a respective squib. The first squib resistor 101 is connected directly between the two poles 104, 105 of a two-pole line equivalent to the two pole line 72. The second squib resistor 102 is connected between the two poles 104, 105 in series with a first voltage drop resistor 106 and the third squib resistor is connected between the two poles in series with two voltage drop resistors 107, 108.

It is to be appreciated that on receipt of an initial triggering pulse, the triggering pulse will pass along the line of least resistance, thus flowing primarily through the squib resistor 101, igniting the pyrotechnic charge associated with that squib resistor. The squib resistor 101 is thus enabled by being in a low resistance path between the two poles, while the remaining squibs are not enabled as they are in high resistance paths. That squib resistor will then go "open circuit". The subsequent triggering pulse will pass through the first voltage dropping resistor 106, and the squib resistor 102, which is now n enabled, thus igniting the pyrotechnic charge associated with the second squib resistor 102. That squib resistor will then go open circuit. A third pulse will pass across the two voltage dropping resistors 107 and 108 before passing through the third squib resistor 103 to ignite the pyrotechnic charge associated with the third squib resistor.

In the embodiments of the invention which have been described above, a central control unit generates an actuating signal which is passed to a local control unit, and the local control unit acts in such a way that the pyrotechnic charges are successively actuated in response to successive actuating signals.

It has been proposed that motor vehicles should be provided with a "bus" control system. In a "bus" control system a central control unit generates coded signals which are supplied to the bus. Each coded signal usually commences with the "address" of a unit or component which is to be controlled by the signal. A plurality of controllable components are connected to the bus, with each component having a decoder to decode the signals present on the bus. When a component decodes a signal which has the address of that component, then the component responds appropriately to the signal. A "bus" arrangement of this type may be used in embodiments of the invention.

Figure 16 illustrates, schematically, a "bus" control arrangement. A central controller 120 is shown, the controller having outputs connected to a bus 121.

The bus may have a first spur 122 which extends to a unit 123 which forms a safety device having an extendible gas driven arrangement of the type described above with reference to the preceding embodiments. The bus may have a further spur 124 which may extend to other parts of the vehicle. In the arrangement presently contemplated the central control unit 120 is associated with a sensor 125 in the form of a crash sensor.

Within the unit 123, four pyrotechnic charges 126,127,128,129 are provided.

Associated with each pyrotechnic charge, and connected to the bus spur 122, is a respective decoder 130,131,132,133.

Each decoder 130,131,132,133 is configured to decode signals present on the bus, and is also configured to respond to a signal from the central control unit 120 which is addressed to the specific decoder. The decoder may be configured to turn on a switch which effectively connects the squib present in the associated pyrotechnic unit directly to a 12 volt supply present in the vehicle, or may close a switch which connects the squib to a capacitor present within the decoder which is charged up by signals received on the bus, again to cause the squib to ignite the pyrotechnic charge.

Thus it is to be understood that in response to an accident situation or a potential accident situation sensed by the sensor 125, the central control unit 120 will initially generate a coded signal addressed, for example, to the decoder 130. The signal will pass along the bus 121 and the bus spur 122 and will decoded by the decoder 130, thus actuating the squib of the pyrotechnic charge 126.

Should a subsequent accident situation be sensed by the sensor 125, the central control unit will then generate a different coded signal, the coded signal this time being addressed, for example, to the decoder 131. Receipt of this signal by the decoder 131 will cause the pyrotechnic charge 127 to be actuated. Thus, in this embodiment of the invention, instead of a local control unit being provided which sequentially enables a series of pyrotechnic charges, the central control unit itself sequentially enables the pyrotechnic charges of the safety device.

When used in this Specification and Claims, 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 components.

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

Claims: 1. A safety device, the safety device comprising an extendible

gas driven arrangement which is actuated on operation of the safety device, at least two individually ignitable pyrotechnic charges for producing gas to drive the gas driven arrangement, a first charge being ignitable to cause an initial cycle of operation of the safety device, and the second charge being actuable to cause a second cycle of operation of the device, there being a central control unit having an output providing an actuating signal each time the safety device is to be operated, the system comprising an arrangement for initially enabling a first pyrotechnic charge to be actuated in response to receipt of the actuating signal and for successively enabling the other pyrotechnic charge (or charges) for receiving the next actuating signal (or signals).

2. A device according to Claim 1 wherein the safety device is a bonnet-lifter (hood-lifter) for protecting pedestrians.

3. A device according to Claim 1 wherein the safety device is a belt tensioner.

4. A device according to any one of the preceding Claims wherein the gas driven device is a piston movable within a cylinder.

5. A device according to Claim 4 wherein the cylinder is divided into first and second chambers by the piston, there being a gas flow path extending between the chambers, the gas flow path having a variable flow resistance.

6. A device according to Claim 6 wherein the piston is configured to change the flow resistance of the variable flow resistance path in response to the piston reaching a predetermined position when moving in a first direction. / 21

7. A device according to any one of Claims 1 to 3 wherein the extendible gas driven device is a telescopic tube having at least one fixed outer tube and at least one movable inner tube.

8. A device according to Claim 7 wherein the telescopic tube comprises two inner relatively movable tubes.

9. A device according to any one of the preceding Claims comprising a local control unit located adjacent to, and individually connected to the pyrotechnic charges, the local control unit enabling a specific pyrotechnic charge to be activated by the next actuating signal.

10. A device according to Claim 9 wherein the output of the central control unit is a two-pole output and the local control unit has a two-pole input connected to the output of the central control unit.

11. A device according to Claim 9 or Claim 10 wherein each pyrotechnic charge is associated with a respective squib having a squib resistor.

12. A safety device according to any one of Claim 11 wherein the local control unit is configured to selectively close closeable switches which are connected respectively in series with respective squib resistors.

13. A device according to Claim 12 wherein the central control unit is configured to generate diagnostic pulses with a low power relative to the actuating signal to diagnose the status of the squib resistors.

14. A device according to Claim 13 wherein the local control unit is configured to be powered by the diagnostic pulses. D 22

15. A device according to any one of Claims 12 to 14 wherein each squib resistor is connected in series with a controllable switch between the two poles of the central control unit.

16. A device according to Claim 15 wherein the switches are controlled from the local control unit.

17. A device according to any one of Claims 12 to 16 wherein the local control unit is configured to sequentially close the switches associated with non-triggered squib resistors for a diagnostic cycle.

18. A device according to any one of Claims 1 to 11 wherein a plurality of squibs are provided each having a squib resistor, the squib resistors each being connected between two poles of a two-pole cable which received the actuating signal, successive squib resistors being associated with successively increasing resistive loads connected in series therewith.

19. A device according to any one of Claims 1 to 8 wherein the central control unit is connected to a bus and provides coded signals to the bus, each pyrotechnic charge being associated with a respective decoder connected to the bus to decode signals from the central controller, the central controller being configured to generate a signal to initially enable a first pyrotechnic charge, so that the change may be actuated, and subsequently to generate a signal (or signals) to successively enable the other pyrotechnic charge (or charges).

20. A safety device according to Claim 1 and substantially as herein described with reference to and as shown in Figures 1 to 9 of the accompanying drawings.

21. A safety device according to Claim 1 and substantially as herein described with reference to and as shown in Figures 10 and 11 of the accompanying drawings.

22. A safety device according to Claim 1 and substantially as herein described with reference to and as shown in Figure 12 of the accompanying drawings.

23. A safety device according to Claim 1 and substantially as herein described with reference to and as shown in Figure 12 of the accompanying drawings.

24. A safety device according to Claim 1 and substantially as herein described with reference to and as shown in Figure 13 of the accompanying drawings.

25. A safety device according to Claim 1 and substantially as herein described with reference to and as shown in Figure 14 of the accompanying drawings.

26. A safety device according to Claim 1 and substantially as herein described with reference to and as shown in Figure 15 of the accompanying drawings.

27. A safety device according to Claim 1 and substantially as herein described with reference to and as shown in Figure 16 of the accompanying drawings.

28. Any novel feature or combination of features disclosed herein.