Safety steering wheel
BACKGROUND OF THE INVENTION 
     This invention relates to a safety steering wheel comprising a cover made of soft elastic plastic and an impact protector which is provided on the hub of the steering wheel and consists of a gas bag, which is collapsed in a position of rest and in response to an impact is suddenly inflatable by means of a compressed gas which is adapted to be produced by a propellant that is accommodated in a housing, and a cover hood which is disposed over the gas bag and is made of soft elastic plastic, in which a reinforcing layer is embedded and which has a rated breaking line. 
     Such a cover hood serves not only to protect the collapsed gas bag and the housing which contains the propellant for inflating the gas bag but is also intended to have a reasonably pleasing appearance. It is known to provide such cover hoods which have a soft elastic plastic layer, which preferably consists of polyurethane foam and is reinforced by woven fabric inserts made of nylon yarns and which has one or more rated breaking lines, along which the plastic layer is torn in response to the activation of the impact protector. The cover hood has on its inside surface an annular peripheral undercut, which receives a suitable shoulder of the carrier for the housing which contains the propellant. To avoid an automatic separation of the cover hood from the carrier for the housing in case of an activation of the impact protector, it is necessary to provide a additional metal strip and to clamp the edge of the cover hood in position between said additional metal strip and the oppositely disposed carrier for the housing which contains the propellant. 
     Since the woven fabric insert by which the cover hood is reinforced consists of a plurality of individual parts, which are made of nylon yarns and have been sewn to each other, it is rather difficult in general to always provide the woven fabric insert in a precisely fitting manner and there is a rather high reject quota. Besides, the placing of the woven fabric insert into the mold during the molding of the cover hood made of soft elastic plastic requires a relatively long time and relatively long standstill periods of the molding machine. Another disadvantage resides in the fact that the reinforcing layer consisting of a woven fabric insert cannot prevent a bulging of the plastic hood under the action of forces exerted by the collapsed gas bag. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide, for the cover hood, a reinforcing layer which has an exactly reproducible, fitting shape and which can be manufactured with relatively simple means and can be placed within a relatively short time into the mold in which the soft elastic plastic is molded around the reinforcing layer. Besides, the reinforcing layer should permanently prevent a bulging of the cove hood. 
     That object is accomplished in that a frame is provided, which is secured to the carrier for the housing which contains the propellant, said frame surrounds the housing and the gas bag and comprises at least one retaining member which is integrally joined to the frame and attached to that edge of the frame which faces the driver&#39;s compartment, said retaining member when in position of rest extends in front of the collapsed gas bag and in case of an impact is adapted to be bent up toward the driver&#39;s compartment along a straight line, and a reinforcing layer is provided, which is made of hard plastic, such as a thermoplastic and covers the gas bag, wherein the rated breaking line of the cover hood that is connected to the frame extends along those sides of said reinforcing layer which are not directly connected to the retaining member. In response to an activation of the impact protector, the plastic layer of the cover hood is torn along the rated breaking line, the retaining member and the plastic reinforcing layer secured to said member are bent up toward the driver&#39;s compartment and the gas bag emerges into the driver&#39;s compartment. 
     A plurality of retaining members are desirably attached to that edge of the frame which faces the driver&#39;s compartment and are integrally joined to the frame by narrow webs. 
     To ensure that the soft elastic plastic layer can be firmly joined to the reinforcing layer of plastic, the latter is formed with numerous apertures, which preferably consist of regularly arranged holes, and the reinforcing layer suitably constitutes a network. The plastic can flow through the apertures to that side of the reinforcing layer which faces the steering column and can form a continuous layer on that side. 
     To ensure that plastic portions of the reinforcing layer joined to the retaining members will not detach from the retaining members upon an activation of the impact protector, the retaining members are formed with apertures in which the plastic of the reinforcing layer is held. 
     The apertures of the retaining members have such a size that the weight of the frame is minimized and the appearance of the cover hood will not be marked by a deformation of the soft elastic plastic in adaptation to the apertures. 
     The frame is connected by conventional fastening elements, preferably blind rivets or screws, to the carrier for the housing which contains the propellant. In a special embodiment the frame is provided with outwardly facing indentations and those portions of the fastening elements which are directed toward the gas bag protrude into said indentations so that a damage to the gas bag by the fastening elements is precluded. 
     The frame and the retaining members attached to it preferably consist of sheet metal in a thickness of from 0.5 to 1.5 mm. 
     The frame has either been formed by deep drawing or has been made from a stamped sheet metal strip, which has been shaped to have a suitable shape and has been soldered and/or welded. 
     The advantages afforded by the invention reside particularly in that the frame, the retaining members which are integrally joined to the frame by webs, and the reinforcing layers which are secured to the retaining members and consist of hard plastic can be exactly made to predetermined dimensions and can be easily placed into the mold which is used to mold the soft elastic plastic layer. Besides, the frame can be molded in a shape which will conform to a cover hood having any desired shape. The retaining members, which extend in front of the gas bag in a position of rest, and the reinforcing layers secured to said retaining members, will very effectively prevent a bulging of the cover hood under the action of forces exerted by the collapsed gas bag. 
     The invention is illustrated by way of example in the drawing and will be described more in detail hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a top plan view showing the impact protector with the retaining members shown broken away and the reinforcing layers secured thereto according to the invention. 
     FIG. 2 is a sectional view taken along section line A--A in FIG. 1. 
     FIG. 3 is a sectional view taken on section line B--B in FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1-3, the substantially rectangular frame 1 consists of sheet steel with a thickness of 0.75 mm and has been formed by deep drawing. The frame 1 surrounds the impact protector, which consists of the collapsed gas bag 2 and a carrier 3 for the housing 4, which contains a propellant for inflating the gas bag 2. 
     A retaining member 5 is attached to each of the two mutually opposite longitudinal bars of the frame 1 at that edge of said bar which faces the driver&#39;s compartment. The retaining members are integrally joined to the frame 1 by webs, not shown. 
     A retaining member 7 is provided at the edge of each of the end bars of the frame and is joined integrally to the frame 1 by a web 6. A reinforcing layer 8 for the covering 9 consisting of polyurethane foam is firmly joined to each of the retaining members 5, 7 and is made of polyamide. 
     The frame 1 and the retaining members 5, 7 are integrally joined and comprise sheet metal having a thickness of from 0.5 to 1.5 mm. The frame 5 is formed from a stamped sheet metal sheet to a suitable shape and has been soldered or welded. 
     Along those sides of the reinforcing layer 8 which are not joined to the retaining members 5, 7, the cover 9 is relatively thin-walled and contains no reinforcement so that the rated breaking lines 10 extend along said regions. 
     The retaining members 5, 7 and the reinforcing layers 8 are formed with apertures 11, 12 so that the polyamide of the reinforcing layer and the polyurethane foam layer of the covering will be held and will be anchored more effectively. 
     The cover 9 may cover the reinforcing layer also on the side facing the steering column. The frame 1 is provided with a plurality of indentations 13 and the blind rivets 14, by which the frame 1 is connected to the carrier 3, protrude into the indentations 13 with those portions of the rivets which are directed toward the gas bag. 
     It will be appreciated that the instant specification and claims are set forth by way of illustration and not limitation, and that various modifications and changes may be made without departing from the spirit and scope of the present invention.