Automotive trim piece and method to form an air bag deployment opening

An arrangement for forming an opening in an auto interior trim panel or piece normally having no visible indication of the opening just prior to inflation of an inflatable air bag, allowing deployment of the air bag into the passenger compartment of vehicle, the arrangement including a linear element positioned below the skin of the trim panel or wheel cover in a pattern corresponding to the opening. In a first embodiment a heat generating element is employed as the linear element which when activated degrades the covering skin layer of the trim piece in pattern shape. In a second embodiment detonating cord enclosed in a metal tube is employed with a series of holes directing the energy of detonation to sever the panel skin material. In a third embodiment a split sleeve having explosive coating on the inside is used to create a flame front severing the panel kin in the appropriate pattern. The skin may be mechanically preweakened prior to assembly by a precision cutting operation performed on the inside surface, in a pattern matching with the pattern of the linear element, aiding the process of forming the opening in the trim piece at the instant of deployment.

BACKGROUND OF THE INVENTION

This invention concerns auto safety systems and more particularly inflatable cushion devices commonly referred to as “air bags”. In such devices, a fabric cushion (the air bag) is stored in a folded condition within a receptacle defining a storage space within the vehicle passenger compartment. Upon activation of a crash sensor detecting an imminent high velocity impact, the air bag is inflated with a chemically generated gas and deployed in a manner and position calculated to absorb the impact of the driver or passenger thrown forward as the vehicle is sharply decelerated at impact.

The folded air bag, gas generator, and other components of the system may be stored within a receptacle mounted in the steering wheel or behind the instrument panel forward of the passenger seat, covered by one or more doors which are opened by pressure generated by the inflating air bag.

The receptacle must be stored in a manner which is tamper proof, yet allowing instantaneous deployment of the air bag upon system activation. Further, the covering must resist normal pressure exerted thereon as by incidental contact with the vehicle occupants.

Prior art systems have typically involved exteriorly visible patterns on the surface instrument panel or steering wheel covers delineating the openings therein through which the air bag will be deployed.

The presence of the visible pattern reduces the aesthetic appeal of the interior trim surfaces and is disturbing to many persons as it makes the presence and possible pending deployment of the air bag obvious. This visible pattern also makes the systems more vulnerable to tampering because of its evident location.

The usual approach in designing a closure is to provide a hinged door latched by a detent mechanism or snap fitted portions forced apart by the pressure of the inflating air bag. See U.S. Pat. No. 4,327,937 issued on May 4, 1982 on a “Downwardly Foldable Covering For a Gas Cushion” for an example of such a covering.

Another common approach is to provide an exteriorly visible line of weakening in a covering skin which is ruptured by the air bag upon deployment. See for examples of such a design U.S. Pat. No. 4,400,010 issued on Aug. 23, 1983 for “Air Bags in Motor Vehicles”, and U.S. Pat. No. 4,334,699 issued on Jun. 15, 1982 for “Cap Like Cover for an Air Bag Installation”.

U.S. Pat. No. 3,640,546 issued on Feb. 8, 1972 for a “Safety Apparatus” discloses a preweakened covering skin over closure doors but the seam skin is unsupported along the seam, and thus the seam would be tactilely perceptible and also, over time, would also become visible due to the absence of any support underneath.

Another approach is described in U.S. Pat. No. 3,632,136 issued on Jan. 4, 1974 for a “Safety Apparatus”, in which a powerful linear shaped explosive charge is used to sever a door lock and reinforcing panel to release a locked door just prior to deployment of the air bag to enable the door to be pushed open by the air bag.

In all of the above designs, the outline of the closure is suggested, and some also result in the showering of debris into the passenger compartment when the system is activated.

Most designs also use separately manufactured and installed covering doors, which increased the cost of manufacture of the air bag installation.

In copending U.S. patent application Ser. No. 07/303,132 filed on Jan. 30, 1989, now U.S. Pat. No. 5,080,393, there is disclosed an invisible closure utilizing a length of detonation cord to create an air bag deployment opening in an interior auto body panel to avoid any suggestion that an air bag is installed therein.

SUMMARY OF THE INVENTION

The present invention provides an invisible air bag installation by the preweakening of the covering layer or skin of a seamless expanse of a trim panel, by cutting a groove into the inside of covering layer in a pattern shaped so as to form a deployment opening immediately above an air bag receptacle mounted behind the trim panel.

The underlying substrate includes a separate door panel fit into an opening in the substrate, so that by preweakening the covering skin, the remaining portions of the trim panel adjacent the pattern are easily able to be pushed aside by inner door panels opened by the expanding air bag to enable deployment through the opening. A degrading of the skin is also carried out by the controlled application of energy.

This preweakening is accomplished by cutting a groove into the inside surface of the skin to a carefully controlled depth to provide for a consistent preweakening of the skin in a matching pattern to augment the effect of activation of the linear element.

DETAILED DESCRIPTION

In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims.

Referring toFIG. 1, major components of an air bag safety system are depicted installed in an automobile. The automobile body10has a passenger compartment12, with various trim panels and pieces finishing the interior thereof.

The air bag system may include a passenger side air bag stored behind an instrument panel14and a driver side air bag stored beneath a steering wheel cover16, the instrument panel14and steering wheel cover16each comprising such an interior trim panel or piece arrayed about the passenger compartment.

Each air bag installation includes a receptacle18containing a folded air bag, which is deployed into the passenger compartment by being inflated with a gas in the manner well known to those skilled in the art. A plurality of crash sensors20are arranged about the front of the vehicle which upon the occurrence of a severe collision, generate electrical signals received by a control unit22, which in turn activates the gas generator contained within the receptacle18.

Since such air bag systems are well known in the art, and the present invention is not concerned with the details thereof a description of these details is not here set out.

Suffice it to say that the gas generators typically are activated by an ignitor assembly24which upon receiving an electrical signal, ignite a chemical charge to produce a high temperature reaction which in turn initiates the chemical reaction producing a large volume of nitrogen gas for inflation of the air bag.

As described above, the air bag must be stored ready for deployment until such collision occurs.

A deployment opening is formed by the controlled application of concentrated energy onto a smooth, uninterrupted expanse of a trim panel, wheel cover, or other piece behind which is mounted an air bag, at the instant of deployment of the air bag.

Such opening is almost instantly formed by the very rapid application to the covering skin therein of energy sufficient to form a line of separation in a pattern shaped to form three sides of a single covering outer door, or of a pair of covering outer doors, with the other side or sides bent by the force of the inflating air bag to act as a hinge to open the door so formed.

The trim panel or piece is constructed so that the remaining portions thereof in the region above the air bag receptacle are sufficiently weakened to be easily severed by receptacle doors pushed open by the air bag itself.

A first embodiment of the energy application arrangement is illustrated in a so-called midmount installation, shown inFIGS. 1-3. A pair of such covering doors are formed at the instant of system activation, the doors28A,28B from a smooth expanse26of the instrument panel14, and each door28A,28B hinged along opposite sides in moving to form a deployment opening.

In this first embodiment lengths of linear thermal generating elements30are embedded in the instrument panel14in the described double door pattern over the air bag receptacle18. A shown inFIG. 3, the elements30are located just below the covering outer layer here comprised of a vinyl skin34. The trim panel such as the instrument panel14is constructed to have sufficient structural integrity to enable assembly and to resist normal contact pressures. Such construction is typically provided by a stiff under layer36of metal or rigid plastic overlain by a layer of soft foam32and covered by the skin34.

According to the concept of the present invention, the under layer36has an opening formed therein shaped to allow the air bag receptacle18to be received thereinto, leaving only the layer of foam32and the skin34above a hinged inner door or doors35covering the receptacle18. Such inner doors35may alternatively be incorporated in the instrument panel14. The receptacle18is mounted as by bracketing (not shown) to be supported beneath the instrument panel14in the position shown in FIG.3.

The thermal generating elements30may comprise a material consisting of two diverse metallic elements in intimate contact with each other. When these elements are subjected to an initiating temperature, a very rapid alloying reaction occurs, in which a great amount of heat is released. Such material in thin wire or ribbon form, comprises an outer core of a palladium alloy and an inner core of aluminum alloy is commercially available under the trademark “PYROFUZE”™ from Pyrofuze Corp. Of Mount Vernon, N.Y.

Preferably, several of these elements each of small diameter, i.e., 0.004 or 0.005 inches thick, are twisted together to generate sufficient heat while maintaining the very high speed reaction required.

This reaction is not explosive and results in a heat degradation of the vinyl skin34in the pattern of the element30sufficient to allow the inner doors35and deploying air bag to push out and separate the adjoining sections of the foam layer32thereof.

The elements30may be directly connected to the air bag ignitor assembly24, thereby insuring coordinated activation simultaneously with the air bag deployment.

An alternate embodiment is shown inFIGS. 4 and 5, illustrated applied to a “topmount” application in which a single outer door42is formed in a smooth expanse44of a horizontal surface of the instrument panel14to allow deployment of the air bag stored in the receptacle18directly beneath the door42.

In this instance, a length of tube46of the desired configuration is positioned within a slot33let into the foam core32, firmly mounted by being secured to one side of the air bag receptacle18with tabs47.

The tubing46has a series of holes52directed outwardly towards the skin34. A length of detonating cord54is disposed within the tube46and detonated by transmission of shock via a connector tube55with the ignitor assembly24of the air bag system itself so as to be simultaneously discharged. The detonating cord54may be commercially available as low power “Primaline”™.

As a result, a series of gas pressure jets are directed to perforate or otherwise degrade the skin34in the pattern outlining the door42so as to allow easy separation of the door42upon contact with the expanding air bag. The confinement of the detonating cord54within the tube46attenuates the intensity of the blast and eliminates the directing of any debris into the passenger compartment.

Yet another embodiment is shown inFIGS. 6 and 7, in which a split sleeve type linear element58is embedded in the foam core32lying beneath the skin34, arranged in a pattern corresponding to the door to be formed. The element58is secured to the receptacle18with formed tabs59. A thin layer of explosive60coats the inside of a plastic tube61. When detonated, a flame front propagates extremely rapidly along the slit62, which is forced open by the pressure generated by detonation.

This flame front very effectively slices through the skin34to form the door through the unmarked expanse of instrument panel14.

Such material is available under the trademark “NONEL” from the Ensign-Bickford Company of Simsbury, Conn.

The invention provides a strong tamper proof covering of the air bag receptacle which is invisible to the vehicle occupants, yet instantly provides an opening for proper deployment of the air bag upon activation of the system. By integrating the covering doors into the trim piece itself, the overall cost of manufacture is reduced and the system is simplified.

The arrangement according to the present invention while illustrated for passenger side air bag installations may also be employed for driver side air bags, by similar design of the steering wheel cover16.

The above described arrangements may also be combined with a mechanical preweakening of the outer layer covering skin34, as depicted in FIG.8.

This preweakening must be able to be accomplished to a uniformly consistent level in production.

According to this aspect of the concept of the present invention, this preweakening is achieved by cutting into the skin34along the inside surface thereof to form a groove66of a consistently controlled depth, and extending in the pattern of the opening to be formed. The groove66thus lies above the linear element.

As noted, it is critical that the partial cutting of the inside of the skin34be consistently held to the designed for depth.FIG. 9illustrates how this can be effectively done. A suitable cutting blade72has mounted to it guide elements74such as rollers adapted to rest on the surface of the skin34as the blade72traverses the skin34. The distance below the surface of the skin34that the cutting edge76protrudes corresponds to the depth of cut, and should be set accordingly.

According to one aspect of this method, substantial compression of the skin material below the cutting edge76should be avoided in order to achieve a consistent depth. This requirement may be met by placing the skin34on a bed of a more easily compressed material than that of the skin, i.e., for example a layer of neoprene rubber77may be placed beneath a vinyl skin. This allows a slight deflection of the vinyl skin away from the cutting edge76to relieve excessive compression leading to erratic and inconsistent results.

The partial cutting of the inside of the skin34can also be varied across the width of the disclosure, from a maximum depth at the center to a reduced depth at either side as shown in FIG.10. This can be done by varying the depth of the cut66, as by a cam control78or other arrangement. This configuration can insure beginning of the tear at the center and propagation to either side.

Thus, the activation of the element30can partially further degrade the skin34(and foam32) in the pattern, with the force of the deploying air bag then mechanically severing the skin34along the preweakening groove66. The reliably severed, combined effect can provide an exteriorly invisible seam forming the air bag deployment opening.