EP1465792A1

EP1465792A1 - Valve for controlled inflation and venting of an airbag

Info

Publication number: EP1465792A1
Application number: EP03729470A
Authority: EP
Inventors: Tuhin Ahmed; R. Farrington
Original assignee: DalphiMetal Ltd
Current assignee: DalphiMetal Ltd
Priority date: 2002-01-17
Filing date: 2003-01-15
Publication date: 2004-10-13
Also published as: AU2003235724A1; GB0201069D0; WO2003059704A1

Abstract

An airbag device having a valve actuator (10) located at the inflation or venting path which is operatively connected to processing means that provide a signal to regulate the inflation or venting in accordance with the accident conditions and/or occupant needs. The valve (10) includes means for regulating the opening of the valve in response to either and inflator or airbag input pressure. The actuation force provided by the valve (10) is generated by a chamber (14) filled with a magnetorheilogical fluid (19) and means for applying a magnetic field to the said fluid (15).The main advantage of this device is that airbag inflation or venting can be achieved.

Description

VALVE FOR CONTROLLED INFLATION AND VENTING OF AN AIRBAG

FIELD OF THE INVENTION

The present invention generally relates to airbags intended for use in vehicles to protect occupants from injury resulting from a collision, crash or other type of accident in which the vehicle is involved. More specifically, the invention relates to airbags with a valve for controlling the inflation and venting accordingly during the airbag deployment of the restraint system. Said valve makes use of magnetorheological fluid to achieve efficiency.

BACKGROUND

Airbags have a limited capacity to protect an occupant during a crash event. Limitations are mainly caused by insufficient control of the inflation or venting after it has been deployed. During an accident the airbag is normally inflated by either, a full release of airbag energy in a single stage process, or by a predetermined split of energy into two stages separated by a time interval. Subsequent venting is highly dependant on the inertial forces of the occupant contact with the airbag. However in the eventuality of such an accident there are many variables affecting the airbags capacity to protect the occupant. These include the size and mass of the occupant, their position immediately before the impact. The most essential variables for a practical control system are the belted or unbelted state of the occupant, the seat position, the type of impact event, and the severity of the vehicle deceleration pulse. As a result the inflation and venting must both be controlled to ensure effective damping of the occupant's inertial deceleration. Appropriate airbag venting is required because an over inflated airbag will cause a bouncing effect on the occupant which would lead to occupant injury. Consequently an under inflated airbag gives rise to occupant injury due to the occupant making contact with the interior of the vehicle. Patent US 5725244 describes an airbag that has a vent that ruptures when the pressure exceeds a predetermined value. Here the venting is controlled by selecting the stitching and material that covers the venting hole.

Patent US 3820814 describes the use of a "discharge valve" which controls the effective area of a discharge aperture as a function of the gas pressure inside of an airbag. The discharge valve located in the walls of the airbag include a cup shaped housing which extends in the outflow direction of the gas and is held by elastic holding elements. This design is such that the housing is displaced by the flow of gas the level of displacement is dependant on the speed of the gas and the direction of the displacement is in the opposite direction of the gas flow.

Patent US 3879057 describes an inflatable vehicle occupant restraint having an exhaust hole which is normally closed by a blocking member which is connected to a restraining member located inside the airbag, the restraining member being responsive to a force exerted on the airbag by a vehicle occupant to open and close the exhaust hole.

Patent US 4360223 describes a check valve, which is used with an inflatable vehicle occupant restraint that has more than one inflation chamber to control pressure differentials between the chambers. This check valve has mating flaps which overly an opening and allow one-way passage of gas through.

Patent US 5016913 describes the use of a heat-shrinking material to overly an exhaust opening in an airbag. The heat-shrink material has a hole therein which grows larger when the material shrinks due to the heat of the inflation gas filling the airbag.

Patent US 5725244 discloses a method of venting an airbag using a gas permeable member located on the airbag, this is illustrated in Figure 1. The gas permeable member is expandable in order to minimize a ventilation opening in the airbag while providing ventilation of inflation gas. The venting member is expandable from a first compressed configuration to a second expanded configuration in response to the inflation pressure in the inflation chamber. When the inflation pressure in the airbag reaches a pre-selected level a selected part of the retaining member breaks and the venting member is expanded through the broken portion of the retaining member by the inflation gas allowing the airbag to vent.

Patent US 5967545 discloses a valve for regulating the pressure of an air bag for a two-wheeled motor vehicle. The valve regulates the internal pressure of the air bag to restrain a rider effectively. The pressure-regulating valve is disposed in a vent hole formed in the air bag. When the internal pressure of the air bag exceeds a predetermined value, the vent hole is opened. When the internal pressure drops to the predetermined value, the vent hole is closed to maintain the airbag in a half-expanded state so that the rider continues to be cushioned against shocks of a crash.

Patent US 6050601 relates to an airbag safety system in motor vehicles, with a gas generator for generating a gas for inflating the airbag and with a slide as a valve member for controlling the inflation of the airbag, whereby the slide is arranged in an intermediate housing between the gas generator and the airbag. However this requires modifying the existing inflation system.

Patent US 6139052 describes a restraint system that includes dual restraints, e.g. airbags, per occupant for each collision event type, such as a front-end collision with another vehicle. A primary airbag responds to crash severity (vehicle speed and deceleration) and a secondary airbag responds to passenger specific parameters, such as weight and orientation. However the disadvantage to this is that the restraint system requires a lot of space, because there is an excess of implemented devices to account for all the situations.

Patent US 6273463 describes a flat cantilever vent valve system airbag pressure control. Here individual vent valve units, located on the outside of an airbag module, provide the necessary total vent area to controllably release inflation gases following deployment of the airbag. The vent valves are normally closed, and are preset to open only at a pre-determined pressure (a venting pressure). Impact of the occupant into the airbag (due to crash acceleration) compresses the airbag causing the internal airbag pressure to rise. As the pressure of the gases within the airbag exceeds the preset venting pressure value of the vent valves, the vent valves open to release the inflation gases. Conversely, as the forward motion of the occupant slows, due to deceleration, the displacement rate slows and the vent valves close as the decreasing pressure of the gases within the airbag approaches the preset venting pressure value of the vent valves. This patent describes a microprocessor controlling a servo controller that opens and closes the vent hole; there is ambiguity if the system can respond efficiently to the crash event.

The limitations of many proposed methods to controlled inflation and venting are that the concepts require either, major modification to the existing restraint system, are too large to fit into the already limited space within a vehicle, or have the potential problem of not responding rapidly enough to the crash event. The majority of the current methods are not active i.e. they are not dependant on external control signals such as type of crash event. Some of the design concepts have the venting hole on the surface of the airbag this gives rise to the problem of filling the passenger compartment with inflation gas, this gas is initially hot so if the occupant is close to the venting hole they could get burned, an additional problem is that the airbag has to unfold before venting can occur. Also the currently available vents cannot be controlled with accuracy and are not flexible to account for all crash events.

This invention relates to the use of a Magnetorheological fluid in a valve for dynamically controlling the inflation or venting during the airbag deployment so we will now describe for reference purposes some of the applications of Magnetorheological fluids in the automotive industry.

To-date Magnetorheological fluids (hereinafter referred to as MR fluids) have been proposed for controlling damping in various devices, such as dampers, shock absorbers, and elastomeric mounts. They have also been proposed for use in controlling torque in clutches and brakes.

Patent US 5632361 describes the application of MR fluid to a damper, which is adapted to be used on suspensions for automotives. The potential problem of such dampers is that on power failure the device would fail to work, a method of using a permanent magnet to avoid this is described. Here MR fluid is located within the chamber of the damper depending on the applied magnetic field and its intensity the bouncing effect of the vehicle can be controlled. A similar principle applies to rotary dampers which can be used for other applications.

Patent EP0940286 describes the properties of the Magnetorheological effect and the accompanying MR fluid to be used in a clutch system. The patent focuses on the potential application to an automotive transmission clutch. Here MR fluid is located between the two member plates on application of the magnetic field the member plates effectively become a single rotary shaft, this is reversed when the magnetic field is removed.

Patent US 6186290 describes a brake system that utilizes Magnetorheological technology. There are two possible configurations for such a brake system the 'annular gap' arrangement and the 'disk-style' brake. This patent describes the annular gap method where the flywheel is encased within a chamber, the MR fluid is located between the flywheel and outer casing. This patent describes the potential application to exercise equipment and automotive brake systems.

Patent DE19848186 describes the controlling of the pedal resistance on an automotive vehicle.

Patent US 601992 describes the MR principles to manage the tensioning of the seatbelt system in a vehicle during a collision.

SUMMARY OF THE INVENTION

A smart restraint system is required to be adaptive to different accident conditions. An airbag that is able to inflate and vent accordingly would not only be more efficient but would also avoid injuring the occupant which sometimes occurs when the occupant is out of position i.e. occupant is too close to the airbag when the airbag is deployed. The aim of this invention is to control inflation and then control the venting of an airbag during a vehicle crash event to maintain the pressure within the airbag as required. The invention will allow deployment of an airbag with the restraint force that is most appropriate for both occupant and crash conditions. The invention may be applied to control the restraint forces required during both impact and rollover vehicle accidents. Because the device controls venting or inflation during a crash event (i.e. frontal, side or rollover), it is possible to efficiently deploy the same restraint device for different crash events. In particular a side curtain airbag can be optimised for side impact and rollover with a minimum of curtain airbag module design change.

To accomplish these and other objectives the present invention provides an airbag device having a valve actuator that can be adapted to both side impact and rollover events. The valve actuator is operatively connected to processing means that provide a signal to regulate the inflation or venting in accordance with the accident conditions and/or occupant need.

The present invention improves on current concepts of airbag inflation/venting by its smaller size, ease of adaptation to the package shape available within a vehicle, electrical control input, rapid time response, and capacity to actuate high gas pressure. The said valve includes means for regulating the opening of the valve in response to either an inflator or airbag input pressure. The actuation force provided by the valve is generated by a chamber filled with a MR fluid and means for applying a magnetic field to the said fluid.

The airbag with a valve actuator according to this invention can be used for both frontal and side airbags. In the latter, an important characteristic of such a valve is its ability to inflate an airbag for up to several seconds in the event of a rollover. An airbag may be sealed so that venting through the fabric and seams does not occur. In the case of a sealed airbag the only venting mechanism is via the valve actuator and this may provide the most efficient control of venting. An alternative is to engineer the relative proportions of fabric or seam venting to the amount of venting remaining under control of the valve actuator.

A primary advantage of using MR fluid for the valve actuator is that it will allow the device to have a small size yet be capable of providing the required actuation force. MR fluids are able to achieve large controlled yield stresses with a relatively small electrical power input. MR devices can be powered directly form low voltage sources and standard electrical connectors and wires can be reliably used. The physical actuation process is effectively instantaneous, in the order of 6 milliseconds. MR fluid is relatively insensitive to temperature extremes and contaminants. MR fluids can operate at temperatures over a wide temperature range with only slight variations in the yield stress.

The benefit of such a device is that active control airbag venting can be achieved. The airbag can be implemented in a vehicle restraint system to match the severity of collision with the restraint energy. This increase in efficiency of the restraint system response means that risk of injury to the occupant is further reduced. Currently oversized airbags are implemented into restraint systems to account for the 'most likely' crash event and maximum sized/weighted occupant. Because the said invention allows the restraint system to respond specifically to each type of occupant, the requirement for oversized airbags is circumvented.

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 perspective view of a known airbag with a vent hole covered by a membrane.

Figure 2 is a plot of the viscosity of the MR fluid for varying shear rates. Figure 3 is a plot which represents the shear stress produced within the MR fluid for a given magnetic field.

Figure 4 is a schematic cross-sectional of a first embodiment of the valve used in the airbag according to the present invention.

Figure 5 is a schematic cross-sectional of a second embodiment of the valve used in an airbag according to the present invention.

Figure 6 is a schematic cross-sectional of a third embodiment of the valve used in an airbag according to the present invention. Figure 7 is a schematic cross-sectional of a fourth embodiment of the valve used in an airbag according to the present invention. Figure 8 is a schematic cross-sectional of the fifth embodiment of the valve used in an airbag according to the present invention.

Figure 9 is a schematic cross-section of the sixth embodiment of the valve used in an airbag according to the present invention. Figures 10 and 11 are schematic views of vent covers controlled by a MR fluid.

Figure12 illustrates the location of the valve used in the present invention when fitted to an airbag.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An airbag system generally includes sensor means for detecting vehicle and occupant accident conditions, a gas generator for releasing gas into an airbag when a signal is received from the sensor means and an airbag that inflates with gas released from the generator. To prevent injury to the occupant the airbag system must inflate the airbag to a pre-determined pressure, provide an acceptable level of ride-down deceleration for the occupant, and maintain that deceleration at a constant value during any crash event. In addition the system would be dynamic enough to account for occupants that are Out Of Position (OOP) and provide acceptable deceleration for occupants whom have varying size/weight.

Figure 1 illustrates a known driver airbag 1 deployed from the steering wheel in the event of an accident. The airbag 1 is inflated with the gas provided by a gas generator 2 in a sudden process that will optimise the maximum inflation volume before occupant contact with the biomechanic injury limit of an occupant in contact during inflation. Then the airbag 1 shall respond to the driver contact with a deflation in a manner that will optimise a biomechanic injury limit with a minimised occupant displacement to either prevent or reduce the severity of injuries from contact with the steering wheel. One known means to achieve this goal is to find a compromise between the gas generator 2 input and the vent hole 3 output covered by a thin membrane 4. The gas discharge through a hole 3 of a convenient size is produced after the rupture of the membrane 4 at a predetermined pressure.

According to the present invention a valve actuator is located at the inflation or venting path of the airbag for controlling the inflation or venting depending on the type of collision and occupant. The electrical input signal to the valve actuator allows the restraining or easing of a gas flow restriction mechanism. The gas restriction mechanism responds dynamically to the through flow of gas and therefore the degree of inflation or venting is dependent on the actuation force to the restrictions. The size and geometry of the restrictions also affect the dynamic flow rate if the inflation or venting gas flow.

MR fluid is used to generate the actuation force as the main means for controlling the gas flow restriction mechanism. MR fluids are (non-magnetic carrier) fluids seeded with magnetizable particles. The host fluid can be any organic fluid. Suitable fluids include silicone oils, mineral oils, paraffin oils, silicone copolymers, white oils, hydraulic oils, transformer oils, halogenated organic liquids. A mixture of these fluids may be used as the host component of the MR fluid. The preferred host fluid is ideally non-volatile, non-polar and does not include any significant amount of water.

Due to the differences in densities of the carrier fluid and magnetizable particles, settling of the particles occurs. Various surfactants and suspension agents are thus added to the fluids to keep the particles suspended in the carrier. Conventional surfactants include metallic soap-type surfactants such as lithium stearate and aluminium distearate. These surfactants typically include a small amount of water, which can limit the useful temperature range of the materials. In addition to particle settling, another limitation of the fluids is that the particles tend to cause wear when they are in moving contact with the surfaces of various parts, so lubricants are also usually added to the host fluid.

Other components include carboxylate soaps, dispersants, corrosion inhibitors, extreme pressure anti-wear additives, antioxidants, thixotropic agents and conventional suspension agents.

Suitable magnetic-responsive particles are iron oxides in particular straight iron powders and reduced iron powders, A preferred magnetic- responsive particulate is carbonyl iron. The particle size is important, generally smaller particle sizes means smaller response time, better sedimentation and is less abrasive.

The rheological properties of controllable fluids depend on concentration and density of particles, particle size and shape distribution, properties of the carrier fluid, additional additives, applied field, temperature, and other factors.

The shear yield stress properties of a given MR fluid can be increased by compressing the MR fluid immediately after the magnetic field is applied. The compression alters the structure of the chains that are formed, the chains formed as a result of compression are thicker. Following "Structure-enhanced yield stress of Magnetorheological fluids, Journal of Applied Physics, Volume 87, No. 5 March 1 2000" if the initial yield stress (in shear) of the given MR fluid is 80kPa this increases 10 fold after the compression technique is applied. Results show that yield stress increases with increased applied magnetic fields as well as compression pressure.

The fluid is non-Newtonian so it cannot be modelled using Newton's viscous flow equation. It only behaves according to Newtonian principles when there is no magnetic field. When there is sufficient magnetic field applied to the MR fluid and its shear yield stress is not exceeded then the fluid will behave as a Bingham solid. If the shear yield stress of the MR fluid is exceeded then the fluid behaves as a Bingham plastic liquid.

The behaviour of the MR fluid can be approximated using Bingham's equations: τ = τ_y +ηχ , τ < τ_y where τ is the yield stress of the fluid τ_y is the field dependant yield stress η is the plastic viscosity of the fluid when there is no magnetic field

γ is the fluid shear rate

Below the yield stress the material behaves viscoelastically: τ = G γ , τ < τ_y where G is the material complex modulus. The reason for the departure from the Bingham plastic equations is because the viscosity (η) is a function of shear rate (γ) and magnetic field (H) as illustrated in the plots illustrated in Figure 2 and Figure 3.

The obtainable shear stress of the fluid is dependant on the applied magnetic field hence the relationship between them is important as shown in Figure 3.

An ideal MR fluid for the application will have, high yield stress, low viscosity, fast response time and stable hysteretic behaviour over a broad temperature range. A typical MR fluid suitable for the valve actuator according to this invention consists of 20-40% by volume of relatively pure, soft iron particles, e.g. carbonyl iron, suspended in an appropriate carrier liquid such as mineral oil, synthetic oil, water or a glycol. For a flux density B~1 Tesla, iron based MR fluids exhibit yield stresses of up to 70 kPa.

We will now explain a first embodiment of the valve actuator following Figure 4. The valve actuator 10 is formed by an outer cylinder 6 having an inlet 11 for receiving the air 20 from the airbag (when the valve actuator is used for controlling venting) or from the inflator (when the valve actuator is used for controlling inflation), a variable outlet 12 for discharging air 25 from the airbag (when the valve actuator is used for controlling the venting) or for providing air 25 to inflate the airbag (when the valve actuator is used for controlling the inflation), a movable piston 13, a MR fluid chamber 14 contoured by coils 15 to generate a magnetic field 24, an air chamber 16 and an intermediate chamber 17 with springs 18. The piston 13 traverses via the bearing and seal 9.

Here the air 20 from the airbag or inflator pushes (arrows 21) against the top of the piston 13 which is then forced downwards, this downward force 23 is resisted by controlling the magnetic field 24 across the MR fluid 19, hence the air

25 escaping from the outlet can be controlled. A small amount of upward force

26 is provided by springs 18. This valve actuator 10 is extremely flexible in its operation. It is possible to open the outlet 12 to a maximum and then block the outlet midway, to hold the airbag at 50% inflation for example. The advantage to this embodiment is that the fluid can be made to have different viscosities at different layers by using more than one magnetic coil. The disadvantage to this embodiment is that the magnetic field is located around a large area, which may mean a higher power requirement.

A second embodiment of a valve actuator according to this invention is illustrated in Figure 5. The valve actuator 30, with the coils 31 being wrapped around the piston 13 is immersed in MR fluid 19. There are circular gaps within the piston 13 to allow the coils 31 to be embedded into the piston 13 with a sufficient number of turns to generate a magnetic field 34, which can provide the restraining force. The coils 31 illustrated are in opposing directions which allow the concentration of the magnetic field 34 to produce sufficient viscosity in the MR fluid, also the cutaway gaps of the cylindrical piston are tapered to reduce saturation. Two coils would allow a sufficient force to be generated however more coils can be included but this requires more space. The restraining force is provided by both the compressing of the fluid as well as the shear stress produced in the selected areas 35 of the fluid volume. The piston 13 is initially in a position that has a closed air outlet 12, preventing air 25 to escape. Air pressure 20, at the inlet 11 from the inflator or airbag vent 11 causes the piston 13 to move through the MR fluid encased in the steel outer cylinder 6. The bearings and seal 9 allow the piston to slide and also prevent MR fluid leaking out. Figure 6 illustrates a valve actuator 40, which is a further embodiment of the said invention. Here two coils 41 are wound around the outer perimeter of the cylinder 6. The two coils 41 are embedded into the cylinder as illustrated to produce the required magnetic field geometry 44. The two coils 41 are wound in opposite directions to concentrate the magnetic field and excite the MR fluid 19, which occurs at locations such as 45. The restraining force is provided by the compression of the fluid and also causing the fluid to become viscous. The piston 13 is initially in a position that has a closed air outlet 12. Air pressure 20, at the inlet 11 from the inflator or airbag vent causes the piston 13 to move through the MR fluid 19 encased in the steel outer cylinder 6. The bearings and seal 9 allow the piston to slide and also prevent MR fluid leaking out. The advantage of this kind of device is that it requires less MR fluid 19. Figure 7 shows another embodiment of this invention. The valve actuator 50 makes use of porous material. It consists of a chamber 14 filled with MR fluid 19, this chamber 51 also houses the porous material 58 placed in the path of the magnetic field 54 as the piston 13 is pushed, it compresses the MR fluid 19 and forces it through the porous material 58; the flow through the porous material 58 is further restricted by applying the magnetic field 54 through it which causes the MR fluid 19 to become viscous at areas 55. The fluid is collected in the collection chamber situated at the other end of the cylinder 6; there is space 51 within the chamber 14 to allow the MR fluid 19 to flow. The piston 13 is initially in a position that has a closed air outlet 12. Air pressure 20, at the inlet 11 from the inflator or airbag vent causes the piston 13 to move through the MR fluid 19 encased in the steel outer cylinder 6. The bearings and seal 9 allow the piston 13 to slide and also prevent MR fluid 19 leaking out. The advantage to this type of design is that there isn't a sliding rod on both sides of the cylinder 6. Also a greater shear resistance is achievable because the (viscous) fluid is forced through a porous material.

A fourth embodiment of a valve actuator 60 according to this invention is illustrated in Figure 8. Here, a bypass tube 61 contoured by coils 62 to generate a magnetic field 64 is incorporated into the MR fluid chamber 14. As the piston 13 moves up and down fluid travels through the bypass tube 61 to replace the fluid displaced. The magnetic field 64 is located along this bypass tube 61 and acts like a valve, on application of the magnetic field 64 the fluid 69 in the region of the field becomes viscous and restricts flow through the bypass tube 61. This restriction of flow effectively restricts the displacement of the piston 13. The advantage to this embodiment is that the magnetic field size is smaller. One disadvantage is the volume of MR fluid required which can lead to an expensive device. Another disadvantage is that the device is slightly larger due to the bypass tube 61.

Another embodiment of the valve actuator is illustrated in Figure 9. The valve actuator 70 comprises a sliding inner tube 71 within another outer tube 72. The pressure 85 from the air 20 entering into the inner tube 71 through the air inlet 11 forces it to slide. The MR fluid 19 in chamber 79 can resist this sliding effect by varying the magnetic field 74 across it allowing control of air discharge 25 through first outlet 75 in the inner tube 71 and second outlet 77 in the outer tube 72. The advantage to this embodiment is that less fluid is utilized; however to compensate for the reduction in fluid, which means that there is less shear resistance available - the shear resistance from the fluid is increased by compressing the fluid in the direction of the field. This leads to the disadvantage of a slightly more complicated set up. Another possible disadvantage to this type of design is that it could be difficult to generate the magnetic field in the required area. The MR fluid can be utilized in a different way by using the MR fluid to hold a cover which could be any material such as a fabric or steel to cover the venting hole.

From Figure 10 it can be seen a cap 96 held to a venting area 93 of an airbag 91 by the MR fluid 92. The applied magnetic field (not shown) creates tension via the MR fluid 92 and holds the cap 96 in place. When the magnetic field is removed, the MR fluid 92' becomes viscous and there is no tension and the cap 96 is pushed away by the inflated air pressure 95 within the airbag. The advantage here is that the arrangement is very simple and very little MR fluid 92 is used. The problem with this embodiment is that the cover and more importantly the MR fluid 92 are lost.

Another embodiment is shown in Figure 11 based on a flap 97 and rotational damper 98 held to a venting area of an airbag 102 by the MR fluid 99. This configuration allows controlled air venting by controlling the MR fluid 99 within the rotational damper 97. This does not take place before the flap is released by removing the magnetic field across the MR fluid 99. Then the flap 97 pushed away by the inflated air pressure 101 , 103 within the airbag. Even though some MR fluid 99 is lost the device is reusable.

The devices particularly illustrated in Figures 4 to 9 can be used to control the inflation of the airbag as well as the venting of the airbag. Figure 12 illustrates its location when it is used for a curtain airbag. The device 110 would be placed in between the inflator 115 and airbag 120, which would allow the device to operate as an inflation device and also as a venting device. This invention can be used to control venting of the various frontal and side airbags within a vehicle. The performance of device would be different for each type of airbag, and the device can be very easily configured to be adapted to each type. To ensure that the airflow path into and out of the airbag occurs only through the device the airbag would have to be non-porous and also sealed. This would prevent 'uncontrolled' leakage and rest total control on the said invention. This invention can be used as both an inflation device and a venting device and may be easily configured to operate as either. The requirement for controlled inflation is that in some cases the restraining force required would be low for example in the case where the occupant mass is low or more importantly where the occupant is out of position meaning that a full airbag inflation would lead to injury caused by the restraint. Operation as an inflation controller removes the requirement of the additional inflator in dual inflation. Depending on the control signals the inflator is fired and the valve according to this invention is used to control the amount of gas pressure entering the airbag, consequently the airbag is deflated according to the control signals. The advantage to the design concepts illustrated in Figures 4 to 9 is that they are very similar to the inflator design in terms of size and construction. The design of the coil allows operation at low currents. Such devices illustrated in Figures 4 to 9 are cylindrical in design.

Compressing the MR fluid increases the device performance; also the device can be optimised by various other methods one example would be by redirecting the flow of vented gas so that it acts on (or balances) the actuation force. The typical response time of this kind of device is about 6ms, and the forces that are generated are stable over a broad temperature range i.e. from -10°C to 120°C.

Claims

1.- An airbag device for motor vehicles comprising an airbag (1) which is inflated in the event of an accident by a gas provided from an inflator, characterized in that it further comprises at least a valve actuator (10, 30, 40, 50, 60, 70) located at the inflation or venting path, having a chamber filled with a magnetorheological fluid (19, 69, 79) subject to a magnetic field (24, 34, 44, 54, 64, 74) for providing a force that regulates the opening of the valve for inflating or venting the airbag, said valve actuator (10, 30, 40, 50, 60, 70) being operatively connected to processing means which provide an electrical current that activates said magnetic field.

2.- An airbag device according to claim 1 wherein the valve actuator (10, 30, 40, 50), is formed by an outer cylinder (6) having an inlet (11) for receiving the gas (20) from the airbag or the inflator, a variable outlet (12), a movable piston (13), a magnetorheological fluid chamber (14) that, at least in a part of it, is contoured by coils (15, 31 , 41 , 51) to generate a magnetic field (24, 34, 44, 54), an air chamber (16) and an intermediate chamber (17) with springs (18).

3.- An airbag device according to claim 2 wherein there are circular gaps within the piston (13) of the valve actuator (30) to allow the coils (31) to be embedded into the piston (13).

4.- An airbag device according to claim 2 wherein the coils (41) are wound around the outer perimeter of the cylinder (6) forming the valve actuator (40) and embedded into it.

5.- An airbag device according to claim 2 wherein the magnetorheological fluid chamber (14) of the valve actuator (50) also houses a porous material (58).

6.- An airbag device according to claim 1 wherein the valve actuator (60), is formed by an outer cylinder (6) having an inlet (11) for receiving the gas (20) from the airbag or the inflator, a variable outlet (12), a movable piston (13), a magnetorheological fluid chamber (14) incorporating a bypass tube (61) contoured by coils (62) to generate a magnetic field (64), an air chamber (16) and an intermediate chamber (17) with springs (18).

1.- An airbag device according to claim 1 wherein the valve actuator (70), is formed by a sliding inner tube (71), having an inlet (11) for receiving the gas (20) from the airbag or the inflator and an outlet (12), within another outer tube (72), having a second outlet (77), and a magnetorheological fluid chamber (79) contoured by coils to generate a magnetic field (74), between said tubes (71 , 72).

8.- An airbag device according to any of claims 1 to 7 wherein the airbag is a curtain airbag (120) and the valve actuator (110) is placed between the inflator (115) and the airbag (120).

9.- An airbag device for motor vehicles comprising an airbag (1) which is inflated in the event of an accident by a gas provided from an inflator, including at least a venting area (93) characterized in that further comprises a cap (96) covering said venting area (93) and a cap actuator having a magnetorheological fluid (92) subject to a magnetic field that, when activated, holds said cap (96) closing said venting area (93) and, when de-activated, releases said cap (96), said cap actuator being operatively connected to processing means which provide an electrical current that activates said magnetic field.

10.- An airbag device for motor vehicles comprising an airbag (1) which is inflated in the event of an accident by a gas provided from an inflator, including at least a venting area (101), characterized in that further comprises a flap (97) and rotational damper (98) covering said venting area (101) and a flap actuator having a magnetorheological fluid (99) subject to a magnetic field that, when activated, holds said flap (97) closing said venting area (103) and, when deactivated, releases said cap (97), said flap actuator being operatively connected to processing means which provide an electrical current that activates said magnetic field.