Safety arrangement for a motor vehicle

In a safety device for a motor vehicle, an air-bag is provided having a gas inlet to receive gas from a gas generator. One or more straps pass from a point on the bag spaced from the gas inlet to a fixed point. Apparatus are provided to release the strap in response to a predetermined signal from a sensor.

BACKGROUND OF THE INVENTION 
THE PRESENT INVENTION relates to a safety arrangement and more 
particularly, relates to a safety arrangement for use in a motor vehicle. 
The safety arrangement comprises an air-bag. 
It has been proposed previously to provide an air-bag in a motor vehicle to 
provide protection for the occupant of a vehicle in the event that an 
accident should arise. Typically, such an air-bag is inflated by a gas 
generator which is activated by a sensor responsive either to an impact on 
part of the vehicle, or to deceleration of the vehicle in excess of a 
predetermined limit. 
It has been proposed previously to provide two gas generators for one 
air-bag (DE-A-4,032,757), only one gas generator being activated if the 
occupant of the vehicle to be protected by the air-bag is wearing a safety 
belt, but both gas generators being activated if the occupant of the 
vehicle to be protected by the air-bag is not wearing a seat belt. It has 
also been proposed to provide an air-bag with two gas generators 
(DE-A-4,341,500), only one of the gas generators being activated when the 
occupant of the motor vehicle to be protected by the air-bag is leaning 
forwards at the moment that the air-bag is to be inflated, but both of the 
gas generators being activated when the occupant of the vehicle to be 
protected by the air-bag is in the correct position. 
If only one gas generator is used to inflate an air-bag that is associated 
with two gas generators, when the bag is inflated it is only "partially" 
inflated, and consequently the position and condition of the bag will be 
very indefinite and uncontrolled. 
SUMMARY OF THE INVENTION 
The present invention seeks to provide an improved safety device. 
According to this invention there is provided a safety arrangement 
comprising an air-bag, gas generator means to generate gas to inflate the 
air-bag, an opening formed in the air-bag connected to the gas generator 
to receive gas from the gas generator, means being provided to restrict 
the movement of at least part of the surface of the air-bag away from the 
opening, the means being releasable in response to a predetermined signal. 
Preferably one or more points on the surface of the air-bag are connected 
by straps or the like to a fixed point, the means being provided to 
release the connection to the fixed point in response to the signal. 
The strap or straps may be located inside the bag or may be located outside 
the bag. 
Preferably a plurality of separate points on the surface of the bag are 
initially connected to the fixed point. 
In one embodiment the plurality of points on the surface are connected to 
the first straps, which in turn are connected to the fixed point via a 
second strap. 
Conveniently both ends of the second strap are initially connected to the 
fixed point, the second strap running through loops provided at the ends 
of the first straps. 
In an alternative embodiment at least the first straps are connected to the 
plurality of points on the surface, one end of each first strap being 
connected to a respective one of a first group of the points, the other 
end of each first strap being connected to a respective one of a second 
group of the points, the first straps being initially slidingly connected 
to the fixed point. 
Preferably the first straps are slidingly connected to the fixed point via 
a second strap. 
Advantageously both ends of the second strap are initially connected to the 
fixed point, each of said first straps thus passing through the loop 
defined by the second strap. 
In one embodiment the means to release the strap or straps comprise a bolt, 
which initially retains the strap or straps in position, and a pyrotechnic 
charge adapted to move the bolt to a strap-releasing position. 
In an alternative embodiment the means to release the strap or straps 
comprise a movable knife adapted to be moved to cut part of the strap or 
straps. 
Preferably the movable knife is associated with a pyrotechnic charge, the 
pyrotechnic charge being adapted to generate gas to move the knife to a 
cutting position. 
In a further embodiment the means to release the strap or straps comprise 
means adapted to burn or melt the straps. 
Conveniently the means to release the strap or straps comprise a housing, 
through which at least one strap passes, the housing containing a 
pyrotechnic charge, the arrangement being such that on ignition of the 
pyrotechnic charge, the strap passing through the housing is burned. 
Preferably the gas generator is adapted to produce either a first volume of 
gas or a second greater volume of gas, the arrangement being such that the 
gas generator produces the second or greater volume of gas in response to 
the signal. 
Advantageously the gas generator comprises a source of compressed gas, and 
means being provided to heat the gas to increase the volume of the gas in 
response to the signal. 
Conveniently the gas generator comprises a pyrotechnic gas generator, two 
pyrotechnic charges being provided, one being adapted to be ignited to 
produce the first volume of gas and the second being adapted to be ignited 
to produce the second or greater volume of gas. 
Advantageously means are provided to produce the signal in response to a 
crash of a predetermined severity, and/or in response to an occupant of 
the vehicle not wearing a safety belt and/or in response to the occupant 
of the vehicle not leaning forward.

DETAILED DESCRIPTION OF THE INVENTION 
In the embodiments of the invention to be described hereinafter, an air-bag 
is provided which is associated with one or more straps, the straps either 
being located on the interior of the air-bag or being located on the 
exterior of the air-bag and serving to confine the maximum volume to which 
the air-bag can be inflated, at least initially. Means are provided for 
releasing the straps, so that the air-bag can then be inflated to a 
greater volume. A sensor is provided to provide a signal to initiate 
inflation of the air-bag when an accident or crash is sensed. The 
releasing means release the straps or the like in response to a specific 
signal produced by a sensor. The sensor may produce the appropriate signal 
in response to a severe accident, or in response to the occupant not being 
restrained by a seat belt, or in response to a situation in which the 
occupant of the vehicle is not leaning forward, although preferably all 
three conditions are present before the signal is produced by the sensor. 
Alternatively, the sensor may additionally be adapted to provide the 
signal in a very severe crash even if the occupant of the vehicle is 
restrained by a seat belt. 
Referring initially to FIGS. 1 and 2 of the accompanying drawings, an 
air-bag 1 is illustrated having a gas inlet 2 which is adapted to be 
connected to a gas generator. The air-bag is provided with, as can be seen 
in FIG. 2, a gas exhaust vent 3. 
The air-bag is initially supplied with a strap 4 which extends from a point 
adjacent the gas inlet to a point 5 on the bag which is substantially 
diametrically opposed to the gas inlet. Consequently the strap 4 extends 
across the interior of the bag. 
It is to be appreciated that when the bag is initially inflated, the point 
5, as shown in FIG. 2, will be retained at a fixed distance from the gas 
inlet 2, thus causing the air-bag to be inflated to a restricted volume. 
Means are provided adapted to respond to an appropriate signal to cut or 
release the strap 4. The released strap 4 is shown at position 4A in FIG. 
1, the bag 1 then being substantially completely inflated. 
It is to be observed that the upper surface of the bag moves through a 
distance .DELTA.h between the partly inflated state achieved before the 
strap 4 is released and the fully inflated state achieved after the strap 
4 is released. 
Consequently the strap 4 serves to minimise the volume to which the bag can 
be inflated. 
FIGS. 3 to 6 illustrate an alternative embodiment which is again provided 
with internal strapping to minimise the volume to which the bag can 
initially be inflated. Referring to FIGS. 3 to 6, an air-bag 10 is 
provided having a region 11 forming a gas inlet. A loop of strap 12 is 
provided adjacent the gas inlet, the loop of strap 12 having eight sliding 
straps, such as 13, 14 of FIGS. 3 to 5 passing therethrough. As seen in 
FIGS. 3 to 5 the sliding straps 13,14 each have both ends 15, 16, 17, 18 
secured to points on the interior surface of the air-bag 10 which are 
located substantially diametrically opposed to the gas inlet 11. Each 
strap has one end secured to a respective one of a first group of points, 
and the other end secured to a respective one of a second group of points. 
The air-bag 10 is shown in a partly inflated state in FIG. 4. It can be 
seen that the straps 13, 14 are substantially taut, and are retained by 
the loop 12. The bag 10 has been inflated to the maximum permissible 
volume at this stage. 
Referring now to FIG. 5 it can be seen here that the loop 12 has been 
released, allowing the air-bag 10 to become inflated to a greater volume 
than as shown in FIG. 4. 
FIG. 6 shows all eight sliding straps 13, 14, 20, 21, 22, 23, 24, 25, all 
of which pass through a single loop 12. The air-bag is provided with an 
exhaust vent 26. The use of sliding straps, as opposed to the use of fixed 
straps, facilitates the initial folding of the bag into a substantially 
flat shape as shown, for example, in FIG. 3. 
FIGS. 7 and 8 illustrate an alternative embodiment in which straps are 
again provided to retain the air-bag, the straps, in this embodiment, 
being located on the exterior of the air-bag. Thus referring to FIG. 7, an 
air-bag 30 is provided adapted to receive gas through a gas inlet 31. A 
plurality of straps 32, 33, 34, 35 are provided which initially pass over 
the exterior of the air-bag, limiting the volume to which the air-bag may 
be inflated. FIG. 8 illustrates the air-bag 30 when partly inflated when 
the straps are in position. Means may be provided to release the strap in 
response to an appropriate signal and the air-bag 30 will then inflate to 
the larger volume illustrated in FIG. 7. 
Various mechanisms may be provided for releasing the straps. 
FIGS. 9 and 10 illustrate one form of mechanism that may be suitable for 
releasing a "loop" strap, such as is shown in FIG. 1 or in FIGS. 3 to 6. 
Referring to FIG. 9, two gas generators 40, 41 are illustrated, mounted on 
a base plate 42. Part of an air-bag 43 surrounding a gas inlet to the 
air-bag is also shown connected to the plate 42. 
Connected to one end of the plate 42 is a fixed end 44 of a loop strap 45. 
The other end of the loop strap 45 forms a folded back and stitched loop 
46. The loop 46 surrounds a bolt 47, when in the initial position 
illustrated in FIG. 9, so that the loop strap 45 is securely anchored in 
position. 
As can be seen from FIG. 10, the bolt 47 shown in FIG. 9 has a central 
part, the two opposed ends of the bolt being retained in co-aligned 
sections of an axial bore 48 defined by two spaced apart housing portions 
49, 50. The bolt is a friction fit and thus does not move axially. 
However, surrounding the head of the bolt in the housing part 49, in a 
cavity 50 provided for the purpose, is a pyrotechnic charge 51. A squib is 
present within the pyrotechnic charge 51, and is connected to a sensor by 
electric leads 52. It is to be appreciated that when the squib is 
activated, the pyrotechnic charge is ignited, thus creating gas which 
drives the bolt 47 axially so that the bolt leaves the housing part 49 and 
is driven to be accommodated completely within the axial bore 48 provided 
in the housing part 50. It is to be appreciated that the loop 46 is then 
disengaged from the bolt 47, meaning that the loop strap 45 is free. 
It is to be appreciated that sliding straps, such as the straps 13, 14 and 
20, 21, 22, 23, 24, 25 of the embodiment shown in FIGS. 3 to 6 would pass 
through the loop straps 45 in such a way that when the terminal loop 46 
becomes disengaged from the bolt 47, the sliding straps are released. 
It is to be appreciated that a mechanism as that shown in FIG. 9 and 10 
could be use to retain the lower end of the strap 4 as shown in FIG. 1, if 
the lower end of the strap 4 is provided with a loop such as the loop 46. 
Similarly, a mechanism of this type could be used to retain the ends of 
the straps 32-35 of the embodiment illustrated in FIGS. 7 and 8, provided 
that those straps each terminate, at at least one end thereof, in 
appropriate loops. 
FIG. 11 illustrates an alternative arrangement for releasing a strap. An 
elongate housing 60 is provided defining a central bore 61. Received 
within one end of the bore is a pyrotechnic charge 62, which is associated 
with a squib 63 connected to wires 64 which pass through a plug 65 which 
seals the end of the bore and retains the pyrotechnic charge in position. 
A piston 66 is provided located adjacent the charge, the piston driving a 
knife element 67. A length of strap 68 extends across the interior of the 
housing 60 at a position in front of the blade 67, the free end 69 of the 
strap emerging from the housing and carrying a loop 70. The loop 70 may be 
connected to one end of a strap 4 as shown in the embodiment of FIGS. 1 to 
3 or the sliding belts 14,16, and 20-25 of the embodiment of FIGS. 3 to 6 
may pass through the loop 70. 
It is to be appreciated that when an appropriate signal is applied to the 
squib 63 through the electric lead 64, the pyrotechnic charge 62 will be 
ignited, generating gas which will drive the piston 66 forwardly, thus 
causing the knife 61 to cut the strap 68, releasing the loop 70 and thus 
releasing the straps connected thereto, such as the straps of the 
embodiments illustrated in FIGS. 1 to 7. 
FIG. 12 illustrates another mechanism for releasing a strap. Referring to 
FIG. 12, an elongate substantially cylindrical housing 80 is provided 
containing, at one end, a pyrotechnic charge 81 which is associated with 
an igniting squib 82 connected to electric leads 83 which pass through a 
plug 84 which seals one end of the housing. 
The other end of the housing is sealed by means of a sealing plug 84. A 
length of strap 85 passes across the cavity 86 defined within the housing. 
When the squib 82 is ignited, in response to a signal supplied through the 
electric leads 83, the pyrotechnic charge 81 is ignited creating a flame 
which burns through the strap 85, or which melts the strap. The free end 
87 of the strap 85, is thus released. It is to be appreciated that the 
free end of the strap 87 may retain a strap such as the strap 4 in the 
embodiment of FIGS. 1 to 2 or may retain straps such as the straps 13, 14 
and 20 to 25 of the embodiment shown in FIGS. 3 to 6, or straps 32 to 35 
of the embodiment shown in FIGS. 7 and 8. 
It is to be appreciated that the strap release mechanism is activated by a 
control arrangement which responds to a sensor. The sensor may produce a 
signal to release the straps in response to a severe crash and/or in 
response to the occupant being unbelted and/or in response to the occupant 
of the vehicle not leaning forwardly. Preferably the straps are released 
only in a severe crash when the occupant of the vehicle is restrained by a 
seat belt and also is not leaning forwardly. 
The gas generator may be adapted to produce a greater volume of gas if the 
signal identified above is produced. There may, as shown in FIGS. 9 and 
10, be two gas generators, one gas generator ordinarily being activated, 
the second gas generator being activated in response to the signal. Thus, 
when the second gas generator is activated the straps are released. 
Alternatively, a single gas generator may be provided using compressed gas. 
If the signal is generated, the volume of gas created by the gas generator 
may be increased by heating the gas. The gas may be heated by using an 
electrical heater or may be increased by using a relatively small 
pyrotechnic charge, which is ignited as gas is released from the source of 
compressed gas, thus heating the gas. 
Alternatively, if a pyrotechnic gas generator is utilised, a first 
pyrotechnic charge may be activated ordinarily and a second pyrotechnic 
charge may additionally be activated in response to generation of the 
signal. 
Referring now to FIG. 13, a sensor arrangement for use with an embodiment 
of the invention is illustrated. 
The sensor arrangement incorporates a sensor 90. The sensor 90 is provided 
with three outputs respectively 91, 92, 93. 
The sensor 90 is adapted to provide an output on the output 91 whenever the 
sensor senses that an accident or impact has occurred. The sensor is 
adapted to provide an output on the output 92 when a severe accident or 
impact has occurred and is adapted to provide an output on the output 93 
when a very severe crash or impact has occurred. Thus the crash sensor is 
sensitive to different degrees of impact and provides initial output 
signals which are dependent upon the severity of the crash or impact 
sensed. 
The first output is illustrated as being connected to a squib 94 which is 
adapted to initiate inflation of the air-bag by activating a first gas 
generator. The squib 94 forms part of the first gas generator, which can 
be a pyrotechnic gas generator and is indicated schematically by the 
dotted line surrounding squib 94. 
The second output 92 is connected to a switch 95, the switch being adapted 
to be open if the occupant of the vehicle is wearing a safety belt. Thus, 
the switch 95 nay be incorporated in the buckle mechanism of the safety 
belt. Alternatively, the switch 95 could be incorporated within the 
retractor mechanism of the safety belt and could be adapted to be opened 
if a predetermined length of safety belt has been withdrawn from the 
retractor mechanism. Of course, if a safety belt is not worn by the 
occupant of a vehicle, ordinarily the great proportion of the safety belt 
is retracted into the retractor mechanism. 
The switch 95 is connected in series with a second switch 96. The switch 96 
is adapted to be open if the occupant of the vehicle is leaning forward 
from an ordinary sitting position. The switch 96, could again be 
incorporated within the retractor mechanism and could be opened if more 
than a predetermined amount of webbing is withdrawn from the retractor 
mechanism. As a person, wearing a safety belt, leans forward, a greater 
extent of webbing is drawn out of the retractor mechanism than the extent 
withdrawn from the retractor mechanism when the person is in an ordinary 
seated position. 
Alternatively, optical means may be provided for determining if the 
occupant of the vehicle is leaning forward, the switch 96 being controlled 
in accordance with the position of the person determined by the optical 
means. The optical means may comprise an optical distance measuring means 
located within the dashboard of a vehicle adapted to determine the 
position of the occupant of the vehicle relative to the dashboard of the 
vehicle, or may comprise means for directing a beam of light transversely 
across the motor vehicle, means being provided to determine if the beam of 
light is broken by a person leaning forward, thus enabling the switch 96 
to be opened appropriately. 
The switch 96 is connected to the parallel connection of a squib 97 
adapted, for example, to activate a second gas generator, and a squib 98 
adapted to activate the means for releasing the strap or straps that 
restrict the movement of the air-bag away from the opening associated with 
the gas generator. Squib 97 is associated with the second gas generator 
which is a pyrotechnic gas generator and is indicated schematically by the 
dotted line surrounding squib 97. Squib 98 is associated with the means 
for releasing the straps, which are indicated by an oval dotted line 
surrounding squib 98. 
The third output 93 of the crash sensor is connected to the node 99 between 
the series connection of the switches 95 and 96. 
It is to be appreciated that in the event that a crash or impact is sensed 
the squib 94 adapted to activate the first gas generator will be 
activated, causing initial inflation of the air-bag. 
In the event that a severe crash or impact is detected, such that an output 
is provided by the crash sensor on the second output 92, if the occupant 
of the vehicle is not wearing a seat belt, and (if an optical sensor is 
provided) the occupant of the vehicle is not leaning forward, then the 
squib 97 to activate the second gas generator and the squib 98 to activate 
the strap releasing means are both ignited. Thus the air-bag is inflated 
to its full extent. It is to be noted that if the switch 96 is activated 
in response to the amount of webbing pulled out from the retractor 
mechanism, if the occupant of the vehicle is not wearing a seat belt, the 
switch 95 will be closed and also the switch 96 will be closed regardless 
of the position of the occupant of the vehicle. Thus, if the occupant of 
the vehicle is not wearing a safety belt, in the event of a moderate crash 
providing an output on the second output 92 of the crash sensor 90, the 
air-bag will be fully inflated 
In the event of a very severe crash, even if the occupant of the vehicle is 
wearing the safety belt, so that the switch 95 is open, nevertheless, when 
an output is present on the third output 93 of the crash sensor, provided 
that the switch 96 is closed (which will be the condition of the switch if 
the occupant of the vehicle is not leaning forward) then again the squibs 
97 and 98 will be activated, causing full inflation of the air-bag. 
It is to be appreciated that whilst, with reference to FIG. 13, reference 
has been made to a squib activating a first gas generator and a squib 
activating a second gas generator, it is to be appreciated that the squib 
97 may instead activate heating means adapted to heat otherwise cold gas 
generated by the first gas generator. 
Whilst the embodiments have been described with reference to embodiments in 
which the strap is initially retained by a strap or straps located inside 
the bag and by a strap or straps located outside the bag, it is to be 
appreciated that in various embodiments of the invention, the strap or 
straps may be connected to one or more points on the surface of the bag to 
connect the said one or more points to a fixed point, or alternatively, 
the strap or straps may each serve to connect a line along the surface of 
the bag to a fixed point. In a further alternative embodiment of the 
invention, the bag may initially be restrained by a net secured over the 
bag and releasably connected to a fixed point, the net being released on 
generation of the signal.