1. The Field of the Invention
The present invention relates to a safety device used particularly in automobiles which, upon the onset of a collision, deploys an inflatable restraint cushion, known as an air bag cushion, to protect the occupants of the vehicle from the impact of the collision. More particularly, this invention relates to an apparatus for protecting the inside surface of an air bag cushion from the hot concentrated gases generated during the deployment of the air bag cushion.
2. The Relevant Technology
An air bag assembly typically includes a diffuser canister that encloses or is attached to a gas generator commonly known as an inflator, at least part of an air bag cushion, and may include a cover which conceals the air bag assembly from view. The air bag assembly is often considered as a module, and the industry is constantly trying to reduce the size of the air bag assembly.
When the vehicle, usually an automobile, is involved in a collision, a crash signal actuates the gas generation inflator to cause the air bag cushion to deploy. Typically, the actuator triggers a chemical or pyrotechnic reaction in the gas generator inflator. The reaction in gas generation inflator produces an inert gas, usually nitrogen, which is directed under pressure into the air bag cushion to force the air bag cushion out of the diffuser canister and into the passenger compartment of the vehicle. In a pyrotechnic-type gas generation inflator, gas is produced by the burning of a gas-generating material.
As the air bag cushion is forced out of the diffuser canister during deployment, the pressure exerted on the cover causes selected portions of the cover to separate in a predetermined manner along tear seams to enable the air bag cushion to be directed into the passenger compartment. As the air bag cushion is directed into the passenger compartment, it is inflated by the continued flow of gas produced by the gas generation inflator. Air bag assemblies are typically installed in the steering column of the vehicle, and another air bag assembly is placed in the instrument panel or dashboard on the passenger side of the vehicle. An air bag cushion is usually made of a synthetic material that is substantially impermeable to the flow of gas.
Initially during the air bag cushion deployment, prior to the air bag cushion rupturing the tear seams of the cover, the gas generation inflator generates a large volume of hot gases under high pressure. The hot gases exiting the gas generation inflator and diffuser canister impact the inside surface of the air bag cushion. This is particularly problematic for the portions of the inside surface of the air bag cushion that are proximate to the apertures formed in the diffuser canister through which the gases exit the diffuser canister and gas generation inflator and enter the air bag cushion. In most cases, the apertures are smooth and round which causes the gas exiting the diffuser canister to be in a concentrated stream of gas. The concentrated stream of gas exits the diffuser canister so quickly at such a high pressure and with such force that the inside surface of the air bag cushion is damaged. When the reaction occurring in the gas generation module creates hot gases, the concentrated streams of gas scorch the inside surface of the air bag cushion and may even bum through the air bag cushion. If a more energetic deployment takes place, the hot gases generated by the gas generation inflator can structurally affect the air bag cushion. Designers of the air bag assemblies have been limited in what type of reactions can be used to deploy the air bag cushion by the temperature and/or pressure of the gases exiting the diffuser canister that can withstand the air bag cushion.
Several different types of changes have been made to the air bag assembly to attempt to solve the problems caused by the concentrated streams of gas damaging the inside surface of the air bag cushion. One attempt to reduce the damage to the inside surface of the air bag cushion has been to add extra linings or layers to the air bag cushion to those areas where the concentrated streams of gas come into contact with the material of the air bag cushion. One type of added layer that has been incorporated in the air bag cushion is a combined heat and energy absorbing bag. The liner is in the form of a fiberglass bag, but is not stretchable or a low porosity bag. This inner bag limits the design of air bag cushions as well as the size that the module can be reduced to. Adding additional layers or linings to portions of the air bag cushion increases the manufacturing steps, the manufacturing time, and the cost of the air bag cushion itself. Additional layers, of even just the synthetic material that the air bag cushion is usually made up of, also increases the amount of space that the stored air bag will require, and becomes a limiting factor when trying to reduce the size of the module.
Other attempts to protect the inside of the air bag cushion have included attaching some type of a deflector on the diffuser canister or making a deflector that is movably positioned between the diffuser canister and the inside surface of the air bag. One deflector consisted of a metal sheet that was formed into an open ended cylinder to act as a heat shield around the diffuser canister. The shield provided protection to the air bag cushion immediately adjacent to the inflator. Another attempt to protect the inside surface of the air bag cushion incorporated a fabric heat shield that was attached to the air bag cushion. When the air bag cushion was deployed, the streams of concentrated gases hit the fabric shield instead of the inside of the air bag cushion. Both of these methods, however, required the use of additional pieces in the air bag assembly. It was particularly difficult, when assembling the diffuser canister and the air bag cushion to insure that the fabric shield was in the right position to intersect the concentrated flow of gases. Both of these deflectors, as well as similar methods, also limited how small the air bag assembly module could be made.