This invention relates to an air bag restraint system, and more particularly to an air bag restraint system which controls the expansion characteristics of an inflatable air bag cushion discharged therefrom such that the inflated profile of the discharged air bag may be varied based upon the size and/or position of the vehicle occupant to be protected and/or upon the severity of a crash event.
It is well known in the prior art to provide an air bag assembly including an inflatable air bag for protecting the occupants of a transportation vehicle. In an automotive vehicle such air bag assemblies are typically located within the hub of the steering wheel and in a recess in the vehicle instrument panel for protection of the vehicle occupants seated in opposing relation to such assemblies. Additional air bag assemblies may be located within the seats and/or door panels for protection of the occupants during a side-impact event. It is also known to utilize inflatable curtain-like structures for deployment from the structural pillars or roof line of the motor vehicle so as to promote restraint and protection of the vehicle occupant during a roll-over event.
Air bag assemblies typically include an inflatable cushion in fluid communication with a gas emitting inflator. Upon sensing certain predetermined vehicle conditions, such as a certain amount of vehicle deceleration, the inflator discharges a fixed amount of inflator gas thereby forcing the air bag into a deployed position. The inflator gas occupies the available volume within the air bag cushion thereby forcing the air bag cushion to expand outwardly to the extent permitted by its construction. The pressure within the air bag cushion upon deployment is proportional to the quantity of inflator gas expelled into the air bag and inversely proportional to the volume occupied by the inflator gas within the air bag. As the occupant comes into contact with the expanded air bag, the inflator gas is forced out of the air bag thereby dissipating the kinetic energy of the occupant.
In some cases, it may be desirable to provide an inflator that has varied levels or stages of inflator gas output in response to the sensing of different vehicle or occupant conditions. Thus, it is generally known in the prior art to provide multi-stage inflators that discharge inflation gas at variable levels depending upon the conditions present during deployment. However, these multi-stage inflators are more complex than typical inflators. Moreover, the use of such multi-stage inflators provides control over only the amount of inflator gas which is discharged and does not provide control over the expanded geometry of the inflated air bag cushion. That is, so long as the air bag has a fixed expanded geometry, the inflator gas will tend to fill the available capacity and the expanded configuration of the air bag will be generally the same even if the quantity of inflator gas is varied although the pressure within the air bag will tend to differ appreciably.
In order to provide an additional degree of freedom in the control of air bag performance, it has been suggested to utilize air bag cushions which incorporate seams within the air bag to control the expanded geometry of the inflated air bag wherein the seams separate upon the introduction of sufficient force across the seams thereby freeing the air bag cushion from the restraint imposed by the seams at lower pressures. In order for such break-away seams to provide controlled expansion, the application of such seams must be performed with substantial precision such that seam separation will occur in a highly reproducible and predictable manner. As will be appreciated, due to the large number of variables involved in the introduction and separation of such break-away seams, such requisite precision and reproducibility may be difficult to achieve.
The present invention provides advantages and alternatives over the prior art by providing an assembly to vary the deployed profile of an air bag cushion which may be inflated to a controlled variable level using either a single stage or multi-stage inflator and which may be expanded preferentially in the depth direction towards the occupant to be protected without the need to rely exclusively on break-away seams. The present invention thereby provides an air bag cushion which may be deployed to a relatively shallow profile during a crash event of low severity or for the protection of a small stature occupant or an occupant seated in close proximity to the air bag and which may also be deployed to a profile of substantially increased depth during a severe crash event or for protection of a larger occupant or an occupant seated further away from the location of air bag deployment. The present invention further provides a mechanism for simply and effectively controlling both the profile of the deployed air bag cushion and the quantity of inflation gas released into the air bag cushion.
Advantageously, according to one aspect this invention provides an assembly to deploy an air bag cushion to a controlled geometry of a depth which is desired in view of the position of the occupant to be protected such that an air bag of substantial depth is available to protect occupants such as larger stature persons who are seated further away from the location of cushion deployment, while a smaller air bag volume of diminished depth is available to protect occupants such as smaller stature persons seated closer to the location of cushion deployment. The deployed profile may also be adjusted based upon the severity of the crash event giving rise to the deployment.
The present invention further provides an effective mechanical actuation mechanism to adjust the deployment characteristics of the air bag cushion which actuation mechanism is not dependent upon a particular cushion construction technique and is activated based upon measured parameters of the crash event and the occupants to be protected.
Furthermore, the actuation mechanism to control the deployed profile of the air bag cushion may be operated either independently or in conjunction with a device to adjust the level of inflator gas which enters the air bag cushion thereby providing additional versatility of operation. Conjunctive operation may be carried out utilizing a single common initiator such as a pyrotechnic squib. Thus, it is a potentially preferred feature of the present invention that the air bag assembly may incorporate as few as two initiators (i.e. one initiator to activate the inflator and one initiator to initiate the actuation mechanism to control the deployment profile of the air bag and the level of inflation gas which enters the air bag).
In addition, the actuation mechanism to control the deployed profile and level of inflation gas may be mounted externally on the inflator or the supporting housing thereby avoiding any need to substantially modify the shape or construction of the inflator housing.
In addition, the actuation mechanism and variable profile air bag of the present invention may be used in conjunction with traditional single stage inflators without requiring internal modifications to such inflators.
These advantages are accomplished in a potentially preferred form of the present invention by providing an inflatable air bag expandable to a first volume and depth which first volume and depth may be restrained to a second diminished volume and depth by tethers which are attached at locations across the surface of the air bag cushion and which are releasably attached to a releasable anchor assembly independent from the air bag cushion. Based upon the severity of the crash event and/or the size and/or the position of the occupant to be protected, an actuation mechanism which releases the tethers from the anchor assembly may be either activated or may remain deactivated to yield a deployed air bag cushion of desired volume and geometric configuration. The volume of inflation gas entering the air bag cushion may be adjusted simultaneously with the profile of the air bag cushion.
According to the potentially preferred form of the invention, the actuation mechanism will remain deactivated in the event that the crash event is of low severity and/or the occupant to be protected is of small stature and/or the occupant to be protected is seated in a position close to the location of air bag deployment, thereby resulting in a constrained final expanded geometry. In the event that the crash event is of sufficient severity and/or the occupant to be protected is of larger stature and/or the occupant to be protected is seated further away from the location of air bag deployment, the actuation mechanism may be activated to at least partially eliminate depth restraint thereby permitting the air bag to expand to a greater volume and depth so as to provide additional cushioning for such an occupant.
Thus, it will be appreciated that variable expanded geometries may be achieved in the inflated air bag with such geometries being controllable and adjustable based upon the severity of the crash event and/or the physical parameters of the occupant to be protected. Such control is preferably achieved through use of one or more mechanical actuation mechanisms which are either activated or deactivated to effect control of the inflatable air bags by either holding or releasing tethering restraint elements from an anchoring location remote from the air bag cushion.
Since the activation or deactivation of the actuation mechanism is carried out in conjunction with deployment of the air bag cushion, the necessary geometric character may be achieved for a given occupant as may be present within the vehicle at the time of deployment. Thus, the variable air bag and actuation mechanism according to the present invention offers substantial versatility in the protection of large numbers of diverse occupants including very small and very large occupants experiencing different levels of crash severity. It will also be appreciated that this system provides a simple, cost effective and highly reproducible system for controlling the volume of deployed air bag cushions even when using a traditional single stage inflator.