The present invention relates in general to automotive air bag systems, and, more specifically, to a hidden air bag deployment door formed by an instrument panel substrate and a molded air bag chute.
Air bag deployment chute assemblies have been put into commercial use for the passenger side of an instrument panel of automotive vehicles. The chute assembly couples an air bag module (typically containing a folded canvas bag and chemical propellants for inflating the bag on command) to a door support panel or substrate of the instrument panel. A typical structure for a chute assembly includes a tubular outer wall, one or more door flaps, a flange surrounding the door area, and one or more hinge members or areas connecting the door flaps to the outer wall and flange.
For styling purposes, it is desirable for the air bag deployment door in the instrument panel to be invisible when viewed from the passenger compartment. In other words, the visible or “Class A” surface of the instrument panel is preferably seamless. Therefore, a pre-weakened seam is required in the substrate (on the “Class B” side) to facilitate tearing open of the door during air bag deployment.
A common material for an instrument panel substrate is injection molded thermoplastic. However, when a tear seam is in-molded in such a substrate, a potential problem occurs that is known as read-through. In read-through, the narrowed thickness of the substrate at the in-molded seam causes visible distortion in the form of a groove on the Class A surface that forms during cooling of the molded material. Therefore, secondary operations have been required such as either 1) laser scoring or milling to cut a pre-weakened seam in the Class B surface that cannot be seen from the Class A surface, or 2) allowing the read-through to occur but then covering the instrument panel substrate with an outer skin layer to hide the read-through seam. The secondary operations increase manufacturing and/or material costs.
Another issue relating to conventional chute assemblies is the need to attach the chute to the instrument panel substrate. One common method to attach a chute has been vibration welding, but the known processes can be costly and it has been difficult to obtain a desired robustness of the attachment.