This application is a divisional application divided from
, which was
published as EP 1580091
. The text of the parent application is reproduced below as Appendix A.
The present invention relates to a pretensioner and particularly
to a pretensioner for a vehicle safety restraint mechanism such as a seat belt.
Traditionally a seat belt safety restraint comprises a
length of belt webbing connected at three points to load bearing parts of a vehicle.
Typically one end is bolted to a door sill on one side of the seat, arranged to
pass laterally across the hips of the seat occupant to a buckle mechanism fixed
to the vehicle on the opposite side of the seat, and then diagonally across the
torso of the seat occupant, via a shoulder support to a retractor mounted on the
B pillar adjacent the door. The buckle mechanism engages a buckle tongue slidably
attached to the webbing.
The retractor fitted at the pillar end of the webbing increases
the comfort for the seat occupant restrained by the belt and allows the webbing
to pay out under relatively low loads to enable limited movement of the restrained
seat occupant, for example to reach in-car entertainment controls or storage compartments.
The retractor is biased to keep the webbing relatively taut about the seat occupant
and a locking element is included to lock the retractor against webbing payout in
the event of a dangerous situation being detected. For example, an acceleration
sensor activates if the vehicle undergoes rapid acceleration or deceleration indicative
of a crash.
In recent years, pretensioners have been introduced to
rapidly pull in a length of webbing to actively tighten the belt about the vehicle
occupant in the event of a crash. This takes up any slack which may have developed
in the belt and helps to more correctly position the vehicle occupant in the seat
to maximise the effect of the belt protection and of any secondary safety restraint
such as an airbag.
Pretensioners comprise a force reservoir such as a pyrotechnically
operated gas generator to provide an impulse of sufficient magnitude to tighten
the belt in a short space of time, ideally before the crash pulse takes full effect.
A typical known pretensioner may use rotational means to wind in a length of seat
belt webbing, for example by rotating the retractor spool on the B pillar in a webbing
rewind direction to take in the required length of webbing prior to the retractor
locking against webbing payout. It is also known to tighten the belt using a pretensioner
attached to the buckle mechanism such as is described in
in which the buckle is pulled back in a vertical direction. In addition,
suggests in Figure 7 a seat belt pretensioning unit at the sill end of
the belt. Such a sill pretensioner is also shown in
describes a mechanism with a pretensioner at the buckle end and at the
sill end with a fastening element below the vehicle seat.
It is desirable for pretensioner arrangements to be as
compact as possible to save space without compromising the capability to pull in
a sufficient length of the seat belt webbing in the event of a crash. However, known
pretensioning arrangements tend to be bulky, and are particularly difficult to use
for the front seats of a three-door vehicle because of the need to allow access
to the rear of such a vehicle past the front seats. Using a traditional retractor
pretensioner mechanism in a front seat of a three-door vehicle causes an unacceptable
Seat travel is greater in a three-door vehicle than in
a five-door vehicle in order to provide such access, and to accommodate this the
door sill end of the webbing is usually attached to a so-called slider bar of well-known
design, instead of being fixedly bolted to the floor. This allows the sill end of
the webbing to be moved longitudinally forward and rearward to facilitate rear seat
access and front seat movement.
It has been difficult to design suitable pretensioners
for use with slider bars and/ or for use in three-door vehicles without obstructing
the function of the slider bar or obstructing access to the rear seats.
One known combination is in
describes a pretensioning device attached to a slider bar which is pivotally
movable in a pretensioning direction in the event of a collision of the vehicle.
The present invention provides an improved pretensioning
According to the present invention there is provided a
pretensioner for a three point seat belt comprising: a cylinder adapted to be attached
to a structural part of a vehicle and a piston disposed within the cylinder; a pyrotechnic
means for moving the piston in a direction that is longitudinal relative to the
cylinder in a pretensioning direction; a slider bar comprising a portion which is
fixedly oriented substantially longitudinally with respect to the vehicle; a seat
belt webbing mounted on the slider bar such that the webbing can freely move along
said portion of the slider bar when the seat belt is not under tension; and a cable
that extends from the piston and is connected to the webbing to cause the seat belt
webbing to move along the slider bar in a pretensioning direction when the pyrotechnic
means for moving the piston is activated.
In this way the sill end of the belt is free to move along
the slider bar when the seat belt is not under tension either from use in restraining
a seat occupant and/or from a pretensioning operation.
Preferably the seat belt webbing is mounted on the slider
bar by looping the webbing around the slider bar; and the cable loops around the
seat belt webbing.
Alternatively, the seat belt webbing is mounted on the
slider bar by looping the webbing around the outer surface of a hollow cylindrical
bobbin or otherwise attaching it to such a bobbin, the cylindrical bobbin being
freely moveable along a portion of the slider bar; and the cable is attached to
the cylindrical bobbin.
Preferably the seat belt pretensioner further comprises
a means for restraining motion of the end of the seat belt webbing in a non-pretensioning
direction following activation of the means for moving the piston.
The pretensioner may be installed in a motor vehicle, such
that the cylinder is connected to a structural member of the vehicle and extends
in a direction that is longitudinal with respect to the vehicle.
Alternatively it may be installed such that the cylinder
does not extend longitudinally with respect to the vehicle. It may be installed
below a seating surface of a vehicle seat.
In one embodiment the cylinder may be connected to a structural
member of the vehicle such that the cylinder extends in a direction that is longitudinal
with respect to the vehicle, and a load bearing webbing guide causes the seat belt
webbing to follow a path that is generally parallel to a line of force that will
be exerted by the pretensioner when the means for moving the piston is activated.
Alternatively the cylinder may be connected to a structural
member of the vehicle such that the cylinder extends in a direction that is longitudinal
with respect to the vehicle, and a load bearing webbing guide is arranged to cause
the seat belt webbing to follow a path that is less than thirty degrees of parallel
to a line of force that will be exerted by the pretensioner when the means for moving
the piston is activated.
Pretensioners can be constructed according to the invention
which make access to rear seats easier, have smaller package sizes and which are
attached to an appropriate sill anchorage zone.
For a better understanding of the present invention, and
to show how the same may be carried into effect, reference will now be made, by
way of example, to the accompanying drawings, in which:
- Figures 1A and 1B are side views of a pretensioner according to a first embodiment
of the present invention;
- Figures 2A and 2B are side views of a pretensioner according to a second embodiment
of the present invention.
As used herein and in the claims terms such as "forward"
and "rearward", "front" and "back" and similar terms are understood to be correlated
to the front and rear of a vehicle in which the seat belt pretensioning apparatus
of the invention is installed. Furthermore, as used herein and in the claims terms
such as "above" and "below", and "higher" and "lower" are understood to be correlated
to the roof and floor of the passenger compartment of a vehicle in which the seat
belt pretensioning apparatus of the invention is installed.
Each of Figures 1A, 1B, 2A and 2B shows a pretensioning
unit 22, a slider bar 10 and a cable 20 for pulling the seat belt webbing 14 in
a pretensioning direction.
The seat belt webbing 14 is of a conventional design and
is attached at one end to a retractor mounted, adjacent a seat, to a load bearing
part of the vehicle such as a vehicle side pillar also known as a B pillar (not
shown). The webbing passes through a web guide also attached to the side pillar
and has a buckle tongue, which is insertable into a buckle (not shown) located on
the other side of the seat, in known manner.
When in use, and tensioned around a seat occupant, the
seat belt webbing 14 is at the forward end of the slider bar 10 in the load bearing
position right hand side as shown in Figure 1A. When the seat belt is not in use
the end of the webbing 14 may be moved in a rearward direction (relative to the
normal direction of movement of the vehicle) as shown by arrow A, along the slider
bar 10 so that it does not obstruct access through the door to the rear seat of
a three-door vehicle.
The cable 20 is preferably of metal and extends from the
pyrotechnic pretensioning unit 22. The unit 22 is of a known type and contains a
piston within a cylindrical housing and a gas generator. The gas generator is pyrotechnically
activated to provide an impulse which forces the piston along the cylindrical housing,
in the direction of arrow A, and pulls the cable 20, pulling the seat belt 14 back
in the direction of arrow A, i.e. in a pretensioning direction.
Prior to pretensioning, the belt 14 is positioned for normal
use at its forward most position, at the right hand side as shown in Figure 1A.
When an acceleration of the vehicle is sensed above a predetermined threshold, a
crash sensor, in known manner, generates a signal indicative of a crash which causes
the pyrotechnic gas generator of unit 22 to fire, creating a tension in the cable
20. The tension in the cable 20 pulls the belt 14 in the rearward pretensioning
direction of arrow A in the region of 50 to 150 mm depending upon the vehicle size
The sudden movement of the belt 14 in the direction of
arrow A takes up any slack in the webbing 14 so as to correctly position a vehicle
occupant within a seat in order to maximise the benefit of the seat belt and correctly
position him for maximum effect of any secondary restraint such as an airbag.
Figure 1B shows the position of the belt 14 immediately
after pretensioning. After the pyrotechnic unit 22 has fired, the piston is prevented
from returning to its original position under the forward momentum of the vehicle
occupant during a crash, by a restraining means.
A ratchet, or other form of non-return mechanism may be
built directly into the pretensioning unit 22 in known manner. For example saw-tooth
shaped projections may be built into the inside wall of the cylinder and a cooperating
tooth attached to the piston to allow the piston to move in the pretensioning direction
A but not the opposite direction.
In Figure 1A the pretensioning unit 22 is located at one
end of the slider bar 10. The webbing 14 is mounted on a bobbin 99 on the slider
bar 10 and in normal use, when restraining a seat occupant, will adopt the forward
position shown in Figure 1A, at the opposite end of the slider bar 10 to the pretensioning
unit 22. A cable 20 connects the piston of the pretensioning unit 22 to the bobbin
99. When a crash sensor indicates that a sudden deceleration or acceleration is
taking place, the pretensioning unit 22 is pyrotechnically activated to pull the
cable 20 and thus the bobbin 99 and the webbing 14 in the pretensioning direction
as shown by arrow A. Figure 1A shows the belt 14 in an unpretensioned position and
Figure 1B after pretensioning. Of course the pretensioning unit 22 could be mounted
in any orientation, for example under or adjacent the slider bar to save space and
cable guides could be fitted to avoid snagging. It may also be mounted in an orientation
transverse rather than longitudinal of the vehicle and/or beneath a vehicle seat.
Figures 2A and 2B show another embodiment of the present
invention. The pretensioning unit 22 is located at one end of the slider bar 10
as in Figures 1A and 1B. However in this embodiment the end of the webbing 14 is
looped directly around the slider bar 10 so as to be freely movable along its length
in normal use, to allow the seat belt webbing to be moved away from the vehicle
door when access is required to rear seats in a three-door vehicle. The cable 20
is connected to the piston in the pretensioning unit 22 and forms a loop which surrounds
the webbing 14 in the region of the slider bar 10. When a crash sensor indicates
that a sudden deceleration or acceleration is taking place, the pretensioning unit
22 causes the looped cable 20 to be pulled in the direction A toward the cylinder
of the pretensioning unit 22, to tighten around the webbing 14 and to pull the webbing
back along the slider bar 10 in the pretensioning direction A to the pretensioned
position shown in Figure 2B.
A load bearing guide can be used to increase the performance
of the pretensioning arrangement and it is preferable to arrange such a guide to
make the webbing 14 travel along a line more parallel and closer to the line of
force exerted by the pretensioning unit 22, thereby increasing the performance.
This increase in performance means that a physically shorter pretensioning unit
22 can be used to achieve the same pretensioning effect, i.e. to pull in the same
length of webbing slack.
According to one embodiment a seat belt guide is fixed
to a load bearing part of the vehicle in such a position that a section of the seat
belt in the vicinity of the pretensioning unit adapts a line angled to the line
of force of the pretensioning unit by less than 30 degrees.
Of course elements of the embodiments described may be
combined. For example the cable 20 could be attached to an arrangement such as a
carriage 16 sliding on a rail 18, as in Figure 1 of
. The pretensioning unit 22 could then be connected to the carriage 16
by another cable and be mounted either in line with, or below, the rail 18.
Appendix A follows, which is the full text and drawings
parent application, published as EP 1580091
. This is included for background information and completeness although
some of the disclosure duplicates some of the description above.