BACKGROUND Safety belts are well known restraining means for motor vehicle occupants.

However, in restraining an occupant in a frontal collision, their interaction with the occupant can induce injuries to the front of the pelvis bone structure, lumbar spine injuries and abdominal injuries caused when the occupant pelvis slides underneath the lap portion of the seat belt during a collision, an event known as submarining.

Additionally, seat belts still allow in many cases, for excessive interaction between the occupants legs, and the instrument panel, with associated injuries to knees and legs, in such collisions.

Load limiting elements and devices such as load limiting mechanisms and pretensioners are well known enhancements to seat belts. Seat belts designed with pretensioners can reduce the amount of interaction between the occupants legs and instrument panel, but do so by increasing the loading on the front of the pelvis bone. Load limiting devices reduce the loading caused by the seatbelt and allow the benefits of early restraint from the belt in a collision when pretensioners are used. Such devices however, allow for a greater risk of submarining. State of the art in motor vehicle seats for protecting the occupant against submarining of the pelvis, and its associated abdominal injuries, comprise of various anti- submarining pans, bars or a combination of these. Such devices are passive structures located underneath the seat foam at the base of the seat. In the event of a collision the inertia of the occupants legs are restrained by these devices, once the seat foam above them has been crushed by the moving occupant. As such,

these devices cannot restrain the occupant until he/she has moved in relation to the seat belt and seat and are of no benefit to the occupant until the occupant has done so. Placing the device closer to the occupant will enhance its performance, but produces comfort problems.

There are also known inflatable devices placed under the seats for lifting its front part in case of collision.

WO 97/29924 discloses a device which raises the front portion of the seat in a collision by active means in order to reduce injuries to lower limbs.

WO 98/41428 discloses a vehicle safety seat comprising a squab having airtight cells in the front portion filled wit resilient foam and means to inflate the cell in response to an accident situation.

GB 2 332 884 A discloses a vehicle safety seat including an inflatable device in the forward part of the squab, mounted under the foam or other padding of the squab, intended to automatically inflate in the event of an accident, raising the knees and restraining the pelvis of the occupant.

All of these devices address one or more, but not all of the above mentioned causes of injury to legs, front of pelvis bone, lumbar spine injuries and abdominal injuries. The introduction of such devices often improves the level of protection (i. e. reduces the injury) for a particular part of the occupant, but in doing so either increases the forces that other parts of the occupant are subjected to, or provide no improvement in protection to these other areas.

The present invention is intended to overcome the drawbacks of the above- mentioned devices by concentrating on managing the energy the entire pelvis of the occupant has in a collision and managing the absorption of said energy in a controlled manner.

SUMMARY OF THE INVENTION The present invention provides a vehicle seat with means to protect his/her occupant in a collision, preventing or reducing the risk of the occupant's pelvis sliding forward excessively with resulting harmful effects due to leg interaction with

the instrument panel and the risk of sliding of the occupants pelvis underneath the lap portion of a seat belt during the collision.

Said means are also intended to restrain movement of the pelvis in conjunction with a seat belt to a greater degree than the seat belt and any passive anti-submarining structure in the seat will achieve together.

Said means are also intended to reduce loading of the pelvis as a result of interaction with the lap portion of the seat belt during a frontal collision According to the invention, there is provided a vehicle seat having inside the squab a pelvis restraining device including a volumetric chamber positioned between the seat structure and the seat foam of the squad and inflation means for inflating said chamber which is activated in the event of a collision.

The device includes means for deploying said volumetric chamber towards the occupant pelvis during its inflation in the event of a collision to prevent excessive forward travel of the occupant pelvis and legs.

The device also includes a lower reaction surface for allowing the sandwiching of the volumetric chamber between the seat foam under the base of the occupants pelvis and said reaction surface at an early stage in the collision.

This device applies a reasonable restraining force to the base of the pelvis at an early stage in the collision and must provide this force throughout as much of the time the occupant moves forward as possible. Ideally, the device would inflate instantly, but to allow for cases where the occupant is slouched, or for other reasons, the occupants pelvis is forward of the normally anticipated design position in the seat, the device will not inflate and provide a restraining force to the base of the pelvis until a small degree of forward travel has taken place (say 15-20mm).

The device must deliver several Kilonewtons of restraining force to the occupants pelvis from this point onwards.

This is in contrast to an anti submarining bar, pan or active anti submarining measure, where the occupant is allowed to move forward in the seat, until restrained by the device which is some distance away from the initial position of the pelvis. In such devices, even if submarining is prevented, the pelvis may be

subjected to unnecessarily high loads at the point of contact with the bar or pan, in order to resist further forward movement.

The invention comprises of a high pressure volumetric chamber that must work at high pressures far in excess of conventional occupant protection airbags (1. 5 Bar and above) and will be unable to use conventional constructions and materials employed in airbag manufacture.

BRIEF DESCRIPTION OF DRAWINGS The features, objects and advantages of the invention will become apparent by reading this description in conjunction with the accompanying drawings, in which: Figure 1 is a schematic view of a vehicle seat with a pelvis restraining device according to the present invention in un-deployed and deployed state.

Figures 2 and 3 show schematically the operation of the device.

Figures 4 and 5 show the main differences between the device according to the present invention and a device known in the art.

Figure 6 is a schematic view of an embodiment of the invention and Figure 7 is a schematic view of the volumetric chamber showing the joints between the panels.

DETAILED DESCRIPTION OF THE INVENTION The pelvis restraining device 1 is formed by a volumetric chamber 2, which is positioned between the seat structure and the seat foam 4.

Such volumetric chamber 2 is filled with gas (arrow G in Fig. 6) from a gas generator 6 like an conventional airbag, and being sandwiched between a lower reaction surface 8 and the upper padding material of the seat 4, displacing towards the pelvis 10 of occupant 12. The occupant 12 interacts with the deployed device 1 squashing it, thus absorbing energy.

According to the invention, when the device is deployed, it extends rearwards, and to a lesser extent upwards within the seat, moving and compressing the seat foam 4 above it and between it and the occupant 12. In it's deployed position 3, the chamber is forced against the base of the occupant pelvis 10 via the seat foam 4 that is sandwiched between the reaction surface 8 and the pelvis 10, to provide early interaction between the device 1 and the occupant 12 in the collision event.

The volumetric chamber 2 includes venting means (not shown in the Figures). As the occupant moves forward under the inertia created by the collision, the chamber 2 is squashed against the reaction surface 8 and the venting occurs (arrow V in Figs. 2 and 3) if needed to absorb energy from the occupant, and to reduce forward movement of the pelvis in relation to the lap portion of the seat belt.

The volumetric chamber 2 may vent allowing the gas to be pushed out of the structure and the direction of the restraining forces produced by the device 1 are controlled by the geometry of the deployed chamber 2-2' (see Fig. 2) or by a combination of the above with the deformation of the reaction surface 8 which may be part of the seat structure (see Fig. 3).

The volumetric chamber may be attached rigidly to the structure elements of the seat structure directly or indirectly or may be independent of it.

We will now describe the main differences of the present invention with respect to the prior art following Figs. 4 y 5 In prior art devices such as the one described in GB 2332884, the occupant 12 travel during the crash excessively forward gaining an acceleration which will at some point 12"be stopped by the anti-submarining means 20. This not only do not avoid the knee 22 contact with the instrument panel 24, but also causes high peaks of pelvis 10"acceleration at the time of contact.

In the case of the device 1 according to the present invention, due to the features of chamber 2 that will be mentioned below, it travels more in space towards the pelvis 10'so that it will couple the occupant 12'at a very early stage providing a more effective restraint.

The location of the folded device 5 is by large defined by the geometry of the seats (which varies all the time) and by the car manufacturer's restrictions and targets. It is common amongst the car manufacturers not to allow that any hard objects occupy the area of the foam base on the seat. There are strict rules regarding minimum relative distances between the pelvis and the hard points on the structure, which restrict the positioning of a packed active device such as the pelvis restraining device according to the present invention.

There is however evidence that the folded device 5 should be located at the front end of the lower structure of the seat and centred in"y"in relation to the occupant (see Fig. 1).

The volumetric chamber 2 may be inflated by means of a gas generator 6 which may be in the form of a motor vehicle airbag gas generator.

The volumetric chamber 2 may be constructed from materials such as a polyamide coated with a thermoplastic such as polyurethane. The properties of a thermoplastic coat allow for welding, given that it melts with the temperature rise and solidifies when it cools down.

The chamber 2 is designed to inflate with an internal pressure in excess of 1,5 bars to provide a rigid or semi rigid platform. This requires materials and constructions for the chamber 2 that are far stronger than those disclosed in the above mentioned prior art and beyond those used in current motor vehicle airbag module assemblies. The chamber 2 may be designed with means of venting the gas, either through it's parent material and or other means including the following: the joins between the material parts of the chamber, one or more venting holes, pressure sensitive burst discs, vents or membranes. The chambers venting mechanism if fitted, may be designed to burst at a pre-determined pressure level, or may be initiated by a second active device.

The chamber 2 is designed to have a pre-determined stiffness, so as to deform in a predictable and/or controllable manner. Such stiffness may also be tuned in conjunction with the design of parts of the seat structure for a more efficient contribution or for a more economical solution.

One embodiment of the pelvis restraining device (see Fig. 6) comprises a bag or chamber 2, an inflator housing 7 having a reaction surface 8, a bracket or other means of fixation of the bag to the inflator housing and of securing the inflator (not shown) and the inflator 6 itself.

The chamber can be made out of any fabric material as far as it provides the functions required for the application. A 940 dtex HT polyamide 66 is an example of such material, but It is also possible to have it made out of other materials and obtain the same levels of strength The fabric should have a coat of a thermoplastic such as a polyurethane to enable the construction of the chamber through welding (I. e. hot bar, high frequency, etc) or through other joining process such as bonding.

The construction of the gas chamber 2 is made in such a way to resist to the high loads caused by the internal pressure. The sheer joint type 9 (see Figure 7) to join the panels (the chamber 2 is made out of two panels 11,13) causes the forces to act in sheer increasing the tear resistance. With such a construction very high pressures (up to 4 bar) can be achieved without compromising the integrity of the chamber.

The volume of the chamber 2 shall preferable be greater to 3 litres to Inflate towards the pelvis over a large area of the seat.

The device needs to use larger side airbag inflators to maintain pressure in the chamber (i. e. 12-15 litres of gas).

Although the present invention has been fully described in connection with a preferred embodiment, it is evident that modifications may be introduced within the scope thereof, not considering this as limited by these embodiments, but by the contents of the following claims.