GB2415665A

GB2415665A - An air bag unit with releasable tethers

Info

Publication number: GB2415665A
Application number: GB0414678A
Authority: GB
Inventors: Fredrik Kaerrman
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 2004-06-30
Filing date: 2004-06-30
Publication date: 2006-01-04
Also published as: GB0414678D0

Abstract

An air bag unit for a steering wheel comprises, an air bag 2, an inflator 3 to inflate the air bag in response to an inflation signal, and a plurality of tethers 4 each attached to the air bag and to a respective releasable anchorage 5, wherein each of the releasable anchorages is configured to release the respective tether in response to an individual actuation signal. A sensor arrangement (20 figure 3) may be provided for sensing the angular position of the steering wheel, and upon detection of an oblique collision one or more of the tethers may be released so that the air bag is inflated in an asymmetric manner (figures 6,7). In this way increased protection is provided by the air bag in a direction towards an A-pillar (17) of the vehicle. Also disclosed is a method of deploying an air bag in response to a signal indicative of an oblique collision.

Description

"IMPROVEMENTS IN OR RELATING TO AN AIR-BAG UNIT FOR A STEERING WHEEL" The

present invention relates to an air-bag arrangement for a steering wheel, in particular an air-bag arrangement for the steering wheel of a motor vehicle such as a car.

It is well known to provide motor vehicles with an air-bag arrangement, mounted in a steering wheel, which, in response to a detected crash impact, deploys to provide protection for the driver from the crash impact.

In many prior proposed arrangements, the entire air-bag unit rotates with the steering wheel. Thus, the air-bag may have any one of an infinite number of possible rotational positions at the instant that the air-bag is inflated.

Consequently, a typical air-bag is axially symmetrical so that the airbag presents exactly the same shape when inflated, regardless of the rotational position of the bag. In this way a predictable cushioning effect is provided.

Whilst an axially symmetric driver's air-bag provides good protection for the driver in the case of a frontal impact, it is been found that in the case of some oblique crash impacts i.e. impacts at an oblique angle to the direction of travel of the vehicle, the driver may still suffer from some injuries. For example, it is envisaged that, in an oblique impact, the head of the driver may move past the symmetrical air-bag and impact with the A-post of the vehicle.

It is a first object of the present invention to seek to provide an improved air-bag arrangement for a steering wheel.

It is a further object of the present invention to seek to provide an improved method of deploying a steering wheel air-bag.

According to one aspect of the present invention there is provided an airbag unit for a steering wheel, comprising an air-bag and an inflator to inflate the air- bag in response to an inflation signal, a plurality of tethers each attached to the air-bag and each attached to a respective releasable anchorage, wherein each of the releasable anchorages is configured to release the respective tether in response to an individual actuation signal.

Preferably, the tethers are equi-angularly spaced about the air-bag.

Conveniently, the tethers are all of equal length.

In a preferred embodiment, the releasable anchorages each comprise a securing bolt for securing said respective tether, a quantity of pyrotechnic material and an igniter for igniting the pyrotechnic material in response to the respective individual actuation signal, wherein ignition of the pyrotechnic material exerts a pressure on the securing bolt sufficient to move the bolt and consequently release the tether.

Preferably, the releasable anchorages and tethers are located within the interior of the airbag.

In one particular aspect of the present invention, the air-bag unit is mounted to the steering wheel of a motor vehicle, there being provided an angular position sensor arrangement configured to detect the angular position of the steering wheel and provide an output signal indicative of said angular position, a control unit further being provided to enable the generation of a selected one or more of said individual actuation signals in response to the output signal indicative of said angular position.

Preferably, the motor vehicle is provided with a crash sensor arrangement, the crash sensor arrangement being configured to detect a particular type of crash impact and generate a signal indicative of the type of crash impact, the control unit generating said one or more enabled, selected individual actuation signals in response to the signal indicative of the type of crash impact.

Conveniently, the crash sensor arrangement is configured to detect an oblique crash impact.

In a preferred embodiment, upon detection of an oblique crash impact, the control unit generates actuation signals in respect of the tethers in close proximity to the A-post of the motor vehicle.

In a yet further preferred embodiment, the control unit generates actuation signals in respect of the tethers positioned in the upper quadrant of the air-bag adjacent the A-post of the motor vehicle.

According to a preferred aspect of the present invention, the crash sensor arrangement is configured to detect a frontal crash impact.

In a further aspect of the present invention, there is provided method of deploying the airbag of a steering wheel airbag unit in response to a signal indicative of an oblique crash impact, comprising the steps of s a) determining the angular position of the airbag unit; and b) in response to said predetermined angular position, releasing at least one of a plurality of tethers, each of which is attached to the airbag and a releasable anchorage, to provide a controlled asymmetric deployment of the airbag.

Preferably, the angular position of the airbag unit is determined prior to receiving the signal indicative of an oblique crash impact.

Conveniently, the instantaneous angular position of the airbag unit is continually determined at time intervals prior to receiving the crash signal.

In order that the invention may be more readily understood, the invention will now be described, by way of example, with reference to the accompanying drawings in which: FIGURE 1 is a diagrammatic cross sectional view illustrating one embodiment of the present invention in which the air-bag unit is illustrated in a non-deployed position, FIGURE2 is a diagrammatic cross sectional view of a releasable anchorage is shown in Figure 1, FIGURE 3 is a diagrammatic cross sectional view of a motor vehicle including an air-bag unit according to the present invention, FIGURE 4 is a diagrammatic plan view of the motor vehicle and airbag unit of Figure 3, FIGURE 5 is a schematic illustration showing the trigger logic for deployment of the airbag unit of Figure 3, to FIGURE 6 is a diagrammatic view from within the interior of a motor vehicle subject to an oblique crash impact, showing the airbag of the airbag unit of Figures l to 4 in a deployed position with one tether having been released as the airbag inflated.

FIGURE 7 is a diagrammatic plan view corresponding to Figure 6, additionally showing the direction of inertial movement of the driver during the oblique crash impact, FIGURE 8 is a diagrammatic view from within the interior of a motor vehicle subject to a frontal crash impact, showing the air bag in a deployed position with axial symmetry, and FIGURE 9 is a diagrammatic plan view corresponding to figure 8, also showing the direction of inertial movement of the driver during the crash impact.

Referring initially to Figure 1, an air-bag unit 1 is provided, which is to be steering-wheel mounted. The unit incorporates an air-bag 2 which, in the non-deployed position shown in Figure 1 is folded in conventional manner.

The air-bag 2 has an inflator 3, which may also be of conventional type, for example in the form of a pyrotechnical unit or a source of compressed gas.

A plurality of tethers 4 are provided, in this case four tethers (of which three are visible in Figure 1) which are located within the interior of the air-bag.

Each tether has one end attached to the air-bag 2 at points which are equi-spaced from each other. The other end of each tether is attached to a respective releasable anchorage 5. The releasable anchorages 5 are each mounted to a circular flange portion of the inflator 3 to releasably secure one end of the tethers 4 with respect to the inflator 3. Although, in the particular embodiment shown in Figure 1, the releasable anchorages are mounted to an integral flange portion of the inflators, it is envisaged that the releasable anchorages might be mounted to any number of suitable surfaces within the air-bag unit 1 to releasably secure the tethers with respect to the inflator. For example, the releasable anchorages might equally be mounted to a separate circular mounting plate (not shown), which may in turn be attached to the inflator. The anchorages are equi-angularly spaced about the inflator and, thus, the tethers are equi-angularly spaced about the airbag 2.

Each releasable anchorage 5 may take any suitable form, provided that it is capable of securing one end of the tethers 4 at a fixed anchor point, in this case adjacent the inflator 3 and, upon actuation in response to an individual pre-determined signal, is capable of releasing the tether as the air-bag inflates.

One releasable anchorage 5 is shown in Figure 2. The releasable anchorage 5 comprises a cylinder 6 defining a cylindrical chamber 7. The chamber 7 communicates, via a passageway 8 with an auxiliary chamber 9 containing a pyrotechnic material 10. An igniter or squib 1 1 is disposed within the auxiliary chamber to ignite the pyrotechnic material 10 in response to an actuation signal.

A bolt 12 has a head portion 13 which is a sliding, sealing fit within the chamber 7 and a stem portion 14 extending axially from the head portion 13 through an aperture 15 in the chamber 6.

The stem 15 passes through the looped end of one of the tethers 4 and the end of the stem portion 15 is frangibly attached to a wall of the inflator 3.

Thus, with the releasable anchorage 5 in its non-actuated position shown in Figure 2, the tether 4 is secured at one end by the bolt 12 in combination with the wall of the cylinder 6 nearest to the tether and the wall of the inflator 3 to which the stem portion 15 of the bolt 12 is frangibly attached.

It will be appreciated that, upon ignition of the pyrotechnical material 10 in response to an actuation signal 32, the head portion 13 of the bolt 12 will be forced in a direction towards the right (in Figure 2), thus retracting the stem portion 15 through the looped end of the tether 4 and releasing the tether 4.

Referring now to Figures 3 and 4, the air-bag unit 1 is shown in a non deployed position mounted to the steering wheel 16 of a motor vehicle 17. As can be best seen in Figure 3, the air-bag unit 1 is mounted within the hub 18 of the steering wheel 16. It will be appreciated that when the airbag unit 1 is so mounted, the air-bag unit 1 is constrained to rotate with rotation of the steering wheel.

An angular position sensor arrangement is provided on the steering column 19 of the motor vehicle 17 which, in the particular embodiment shown in Figure 3, is in the form of an optical sensor arrangement 20. The optical sensor arrangement 20 is configured to detect the angular position of the steering column 19 supporting the steering wheel 16, and therefore the angular position of the steering wheel 16 and air-bag unit 1. The optical sensor arrangement 19 comprises a code disc 21, mounted to the steering column 19, and an optical sensor unit 22 comprising a light emitting portion 22A and light receiving portion 22B disposed on opposite sides of the code disc 21.

The code disc 21 comprises a pattern of apertures or notches, which may be in the form of, for example, two separate concentric tracks of apertures with the apertures forming one track being universally off-set with respect to the corresponding apertures forming the other track.

It will be appreciated that rotation of the steering column 19 intermittently allows the transmission of a light beam from the light emitting portion 22A, through the apertures, to the light receiving portion 22B and, furthermore, that the intermittent transmission of light through the two tracks of apertures as the code disc rotates will provide two square wave output signals (one corresponding to each track) which, due to the tracks of apertures being offset with respect to one another, will be out of phase.

The optical sensor 22 is provided with a processor (not shown) which comprises two output channels, one for each square wave signal, and which "counts" the number of pulses contained within each of the two output signals, to determine the degree of angular rotation of the steering wheel 16 with respect to a pre-determined initial angular position of the steering wheel 16.

Moreover, the processor also determines the relative phase of the two output signals to determine the direction of rotation of the steering column 19, steering wheel 16 and hence air-bag unit 1.

Thus, optical sensor arrangement 20 provides an output signal 23 which is indicative of the angular position of the steering wheel 16 and air-bag unit 1.

Referring again to Figures 3 and 4, a crash sensor 24 is provided to sense a frontal impact comprising a frontal crash impact sensor in the form of an accelerometer 25 positioned at the front of the vehicle, with its axis of sensitivity aligned with the axis of the vehicle. Two oblique impact crash sensors, in the form of accelerometers 26 and 27, are located at either side of the motor vehicle 17. The accelerometers 26 and 27 have their axes of sensitivity extending obliquely to the longitudinal axis of the motor vehicle 17.

Thus they are configured to provide an output signal in response to an oblique impact within a pre-determine range of angles relative to the axis of the vehicle.

Upon detection of an acceleration of the motor vehicle in the relevant direction during a crash impact, accelerometers 25, 26 and 27 generate output signals 28, 29 and 30 (see Figure 4), each signal being indicative of the magnitude of the acceleration detected by the respective accelerometers 25, 26 and27.

A control unit 31 is provided within the motor vehicle, which may be in the form of a separate, dedicated control unit or which may form part of the central electronic management system of the motor vehicle 17. The control unit is configured to receive each of the output signals 28, 29 and/or 30, as well as the output signal 23 indicative of the angular position of the steering wheel 16 and, in response to the signals, to subsequently provide an inflation signal on a bus line 32 to the inflator 3 to deploy the air-bag 2. In addition, the control unit 31 is configured to provide one or more individual actuation signals on the bus line 32 to actuate a selected one or more of the releasable anchorages in response to a detected oblique impact, the selected releasable anchor or anchorage being selected in dependence upon the determined angular position of the steering wheel.

The operation of the air-bag unit 1 within the motor vehicle 17 will now be described with reference to Figure 5, which shows the principal components of the air-bag unit system within the motor vehicle 17 and, in particular, the trigger logic employed by control unit 31 to deploy the air-bag 2 of the air-bag unit 1 in a crash situation.

As the motor vehicle travels along a road, the optical sensor arrangement 19 continually determines the angular position of the steering wheel 16 of the motor vehicle 17 and generates a series of output signals 23 indicative of the instantaneous angular position of the steering wheel 16. Each of the signals 23 is received by the control unit 31 and, on the basis of the detected instantaneous angular position of the steering wheel, the control unit 31 performs logic step 33 (see Figure 5) to identify which of the tethers 4 are in the close proximity of the A post of the motor vehicle 17 and, preferably, which of the four tethers is in the upper quadrant of the air-bag 2 adjacent the A post of the motor vehicle 17. The releasable anchorage of the or each identified tether is thus enabled by the control unit, so that if an oblique crash is sensed, the or each identified anchorage may be immediately released.

Upon a crash impact on the motor vehicle 17, the control unit 31 receives one or more of signals 28, 29 and 30 from the accelerometers 25, 26 and 27 respectively and, in response to signals 28, 29 and 30, performs logic step 34 to determine whether or not the crash impact angle is representative of an oblique crash impact, being an impact between around 25 to 35 degrees, and in particular 30 degrees, to the longitudinal axis of the motor vehicle or a frontal impact, being an impact between around O to 25 degrees, and in particular O degrees, to the longitudinal axis of the motor vehicle.

In the case where the control unit 31 determines the angle of the crash impact to be representative of an oblique crash impact 35, the control unit assess whether or not the deceleration of the motor vehicle detected by accelerometers 26 and 27 is sufficient in magnitude to warrant deployment of the air-bag 2 of the air-bag unit 1. In the case where the control unit determines that deployment of the air-bag is in fact required, the control unit proceeds to logic step 36 and operates to release the pre-identifed tether or tethers by providing an actuation signal 37 to the or each enabled releasable anchorage 5.

In addition to step 33, the control unit proceeds to carry out logic step 38 and provides the inflation signal to the inflator 3, to inflate the air-bag 2.

Thus, in the case of an oblique crash impact, the tether or tethers 4 in close proximity to the A post of the motor vehicle 17 are released as the air-bag 2 inflates, with the result that the air-bag 2 inflates in an axially asymmetric manner. The part of the airbag retained by the unreleased tethers forms a generally flat "cushion" 41, but the part of the airbag with released tethers 42 extends upwardly to cover a substantial portion of the A post of the motor vehicle, as best shown in Figure 6. It will be appreciated that, upon adopting the asymmetric shape illustrated in Figure 6, the air-bag 2 thus provides a cushioning effect in the direction of inertial movement A (see Figure 7) of the driver towards the A post in an oblique crash impact, thereby reducing the risk of injurious impact of the driver with the A post of the vehicle.

In the alternative case where, at step 34, the control unit 31 determines the angle of crash impact to be representative of a frontal impact 39, the control unit proceeds to logic step 40 to determine whether the magnitude of the deceleration of the motor vehicle 17 is sufficient to warrant deployment of the air-bag.

In the case where the control unit determines that the deceleration of the motor vehicle 17 is sufficiently severe to warrant deployment of the air-bag 2, the control unit 31 then proceeds directly to logic step 38 and triggers deployment of the air-bag 2 by providing the inflation signal 32 to the inflator 3.

In the case of a frontal impact, no actuation signals 37 are generated (see Figure 5).

Thus, in the case of a frontal crash impact, the air-bag is deployed with effectively a conventional steering wheel airbag trigger logic and, in particular, all of the tethers 4 remain attached at one end to the airbag 2 and secured at the other end to their respective releasable anchorages 5 throughout the inflation of the air-bag 2. Thus, given the equal length and equi-angular spacing of the plurality of tethers 4 about the inflator 3 (and hence air-bag 2), the air-bag 2 inflates in an axially symmetric manner, as in the case of a conventional frontal impact steering wheel air-bag, as shown in Figure 8, forming a generally flat "cushion" 43. l bus, in the case of a frontal crash impact, the airbag 2 provides a cushioning effect in the direction of inertial motion B (see Figure 9) of the driver towards the steering wheel 16 of the motor vehicle 17 and hence reduces the risk of injurious impact of the driver with, for example, the steering wheel 16 of the motor vehicle 17.

Although, in the present embodiment only four tethers are provided on the airbag, it is envisaged that the number of tethers provided may be varied as appropriate; for example, eight tethers may be provided in which case eight respective releasable anchorages S would be provided at 45 angles around the flange portion of the inflator 3. Indeed, it is envisaged that the plurality of tethers might also be positioned at irregular angular intervals about the air-bag.

The air-bag may be provided with a multi-stage gas generator controlled to generate a first volume of gas in a frontal impact to inflate the air- bag appropriately, and a larger volume of gas in an oblique impact to ensure that the air-bag with the released tether(s) inflates to an appropriate pressure.

While the releasable anchorage has been described as a releasable bolt, alternative releasable anchorages which include a pyrotechnically driven knife to cut a tether, or a flame producing pyrotechnic unit to burn through a tether may be used.

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 s

1. An air-bag unit for a steering wheel, comprising an air-bag and an inflator to inflate the air-bag in response to an inflation signal, a plurality of tethers each attached to the air-bag and each attached to a respective releasable anchorage, wherein each of the releasable anchorages is configured to release the respective tether in response to an individual actuation signal.

2. An air-bag unit according to claim 1, wherein the tethers are equiangularly spaced about the air-bag.

3. An air-bag unit according to claims 1 or 2, wherein the tethers are all of equal length.

4. An air-bag unit according to any preceding claim wherein the releasable anchorages each comprise a securing bolt for securing said respective tether, a quantity of pyrotechnic material and an igniter for igniting the pyrotechnic material in response to the respective individual actuation signal, wherein ignition of the pyrotechnic material exerts a pressure on the securing bolt sufficient to move the bolt and consequently release the tether.

5. An airbag unit according to any preceding claim, wherein the releasable anchorages and tethers are located within the interior of the airbag.

6. An air-bag unit according to any preceding claim, wherein the air-bag unit is mounted to the steering wheel of a motor vehicle, there being provided an angular position sensor arrangement configured to detect the angular position of the steering wheel and provide an output signal indicative of said angular position, a control unit further being provided to enable the generation of a selected one or more of said individual actuation signals in response to the output signal indicative of said angular position.

7. An air-bag unit according to claim 6, wherein the motor vehicle is provided with a crash sensor arrangement, the crash sensor arrangement being configured to detect a particular type of crash impact and generate a signal indicative of the type of crash impact, the control unit generating said one or more enabled, selected individual actuation signals in response to the signal indicative of the type of crash impact.

8. An air-bag unit according to claim 7, wherein the crash sensor arrangement is configured to detect an oblique crash impact.

9. An air-bag unit according to claim 8, wherein, upon detection of an oblique crash impact, the control unit generates actuation signals in respect of the tethers in close proximity to the A-post of the motor vehicle.

10. An air-bag unit according to claim 9, wherein the control unit generates actuation signals in respect of the tethers positioned in the upper quadrant of the air-bag adjacent the A-post of the motor vehicle.

11. An air-bag unit according to claims 8 to 10, wherein the crash sensor arrangement is also configured to detect a frontal crash impact.

12. A method of deploying the airbag of a steering wheel airbag unit in response to a signal indicative of an oblique crash impact, comprising the steps of: a) determining the angular position of the airbag unit; and b) in response to said predetermined angular position, releasing at least one of a plurality of tethers, each of which is attached to the airbag and a releasable anchorage, to provide a controlled asymmetric deployment of the airbag.

13. A method according to claim 12, wherein the angular position of the airbag unit is determined prior to receiving the signal indicative of an oblique crash impact.

14. A method according to claim 13, wherein the instantaneous angular position of the airbag unit is continually determined at time intervals prior to receiving the crash signal.

15. An airbag unit according as described herein with reference to Figures 1 to 9.

16. A method as described herein with reference to Figure 5.

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