Abstract:
The frame of the automobile vehicle seat back comprises a body extending over a general plane and functional components joined to the body, serving notably to attach or reinforce it. It is made in one piece from an overmoulded plastic material that forms the body, reinforced by a reinforcing strip comprising a woven band of mineral and plastic material fibers, the reinforcing strip extending in the general plane of the frame and interconnecting at least two of the functional components comprising inserts at least partially embedded in the body.

Description:
RELATED APPLICATIONS 
   The present application claims priority under 35 USC §119 to a French national patent application, FRANCE No. 0307521, filed Jun. 20, 2003, and entitled “Automobile Vehicle Seat Back Frame, and Process for Manufacturing such a Frame.” 
   FIELD OF THE INVENTION 
   This invention concerns the domain of the automobile seat, and more specifically a frame forming the back of an automobile seat, and its manufacturing process. 
   Conventionally, these frames are made from metal tubes and sheets that are generally formed by bending, piercing, drawing and welding. These operations, however, require several successive operations performed at different workstations, which complicates manufacture and necessitates transfers from one workstation to the next. This also creates a large amount of waste in the raw materials used, and in the tube and sheet metal offcuts. 
   Moreover, frame reworks are necessary to add particular functions such as the attachment of a seat back hinge to the seat pan or the attachment of means to support a headrest, etc. 
   In addition, reinforcing parts have to be added, when the stresses the frame might be subjected to so require for reasons of safety, for the attachment of safety belts or the attachment of an infant seat, for example. Such reinforcing parts increase the number of parts to produce and manage, increase the weight of the seat and result in additional assembly operations. 
   We also know from document EP 0372339 for example, of seat back frames made from injected plastic, in which the side vertical members and the upper crosspiece are made from U-shaped sections, with the sections of the vertical members opening to the exterior of the seat and featuring reinforcing ribs in the interior of the U-section. Moreover, the bottom ends of the vertical members are provided with reinforcements for attaching the means of joining the seat back to the seat pan and enabling it to be folded down, but no information on the method of producing and using these reinforcements, and the strength of such joining means, even if locally reinforced at the bottom of the side vertical members, risks being insufficient to withstand the heavy loads applied to the seat back. More specifically, only the plastic material of the seat back ensures the joint between the two reinforcing parts at the bottom of the vertical members, and cannot reliably prevent these vertical members from separating and being pushed apart, if subjected to high loads in an accident, for example. Furthermore, the seat back presented is made from several parts because the moulding of the ribs in the vertical members requires the members to be open, therefore they must be closed by covers after moulding the frame to conceal the ribs and provide a finish to the frame. 
   SUMMARY OF THE INVENTION 
   The aim of the invention described herein is to solve these problems, and more particularly to replace the traditionally known seat back frames by frames based on composite plastic material, bringing reductions in weight and cost and in the number of parts, and facilitating integration of the various functions that might be desired. 
   With these objectives in mind, the subject of the invention is an automobile vehicle seat back frame, featuring a body extending in a general plane and produced as a one-piece moulded plastic part, and functional components associated with the body, in particular to attach or reinforce it. 
   In accordance with the invention, the frame is characterized in that the body of moulded plastic material is reinforced by a reinforcing strip comprising a woven band of mineral and plastic material fibres; the reinforcing strip extending in the general plane of the frame and interconnecting at least two of the functional components that comprise inserts at least partially embedded in the body. 
   As will be more clearly understood later, such a structure is particularly easy to produce, since it is formed from a single part and can provide for significant weight savings without sacrificing mechanical strength, particularly at the location of the attaching or reinforcing components. Indeed, a common problem encountered in the production of such composite structures for diverse applications is the joining of the inserts—which serve to fulfill various functions and are usually made of metal—with the plastic material which overmoulds, at least partially, the inserts. 
   The functional components required for an automobile seat back include the frame attaching components such as hinges to allow the seat back to pivot on the seat pan, or components for attaching the upper section of the seat back to the vehicle chassis. The components can also be reinforcing parts, located at points where the frame risks being particularly heavily stressed, such as in the safety belt locking or attachment zones, etc. Overmoulding of the inserts that constitute these components with the plastic material certainly maintains their relative position but does not necessarily provide a very strong joint, particularly with respect to tensile stresses, between the various inserts overmoulded in the same structure. 
   The use of the reinforcing strip in accordance with the present invention to connect these various inserts considerably increases their strength, taking advantage of the very strong mechanical reinforcement provided by the constituent fibres of the woven strip. More specifically, the strip can be positioned around the frame, such that it interconnects the various inserts, as a continuous loop, the ends of the strip being firmly joined together and this joint being reinforced by the overmoulding of the plastic material of the body, thereby providing a connection between the inserts that displays very high tensile strength to prevent the inserts from being separated from one another. 
   Furthermore, the flexibility of the woven band, which resembles a flat strap, means that it is easy to put in place during manufacturing, by interconnecting the various inserts that are propositioned and held in position in a manufacturing supporting frame before moulding the plastic material of the seat back over the assembly. 
   The reinforcing strip is preferably a woven band comprising glass fibres and thermoplastic fibres, particularly in polypropylene (PP) or polyethylene terephthalate (PET), as is the case for example in TWINTEX®, which combines high tensile strength and good impact and temperature resistance with a high level of rigidity. 
   The plastic material that overmoulds the strip and the inserts to form the body of the frame can be thermoplastic or thermosetting. The preferable choice will be a PET roving filled with glass fibres. The materials shall be chosen so that the resulting seat back can be recycled if necessary. 
   In a particular arrangement, the inserts interconnected by the reinforcing strip are at least partially inserted into the body of the seat back frame and feature obliquely angled slits or cutaways through which the reinforcing strip is passed. Each insert constitutes a change-of-direction point for the strip, that is to say that an end of the strip passed through the slit or cutaway in a roughly horizontal direction, for example, will leave it in a roughly vertical direction, which can, for example, allow one and the same strip to be used to connect inserts situated in the four corners of a rectangle corresponding to the basically rectangular shape of the seat back. The strip can of course also be arranged, instead of or in addition to, the rectangular configuration described above, in diagonal, transverse or oblique directions, etc., to interconnect inserts located in diagonally opposing positions on the seat back, for example. 
   In another configuration, the inserts interconnected by the reinforcing strip are made from suitably bent metal wire featuring oblique sections around which the reinforcing strip is passed, and possibly protruding parts, with the oblique sections constituting the change-of-direction points, in a similar manner to that described above. 
   In particular cases of course, the strip can also be passed over, through or around any elements of these inserts in other directions, or one end of the strip can be secured to them by a buckle. These different configurations will depend on the shape of the seat back and the directions of the stresses exerted on the seat back frame as a whole and on the inserts. 
   These parts can be made from sheet metal cut to shape, bent wire, parts prefabricated by moulding or other processes in diverse metallic or non-metallic materials. 
   Plastic material can be moulded at the same time as the frame body over the protruding sections of the inserts to constitute functional parts, such as trunnions for attaching and/or pivoting the seat back at its base. In this case the protruding section of the insert constitutes an internal reinforcement of the trunnion, which itself is essentially formed by the plastic material that encapsulates the protruding section. In other cases the plastic material could be moulded over the insert to provide a coating of limited thickness encapsulating the protruding section of the insert. 
   The term protruding sections as used herein means sections that protrude locally with respect to the general outline of the frame body. 
   The protruding sections of these parts can also be left bare, that is to say not coated with plastic material, to constitute attaching components, either for attaching the seat back to the seat pan or the vehicle chassis, or to permit the temporary or permanent attachment of other components or add-on accessories to the seat back frame, such as headrests, removable infant seats, etc. 
   In a complementary configuration, a closing plate is fixed to the body of the composite frame, preferably by welding, to constitute the rear surface of the seat back. This plate is prepared independently of the frame and is preferably made from a fibre-reinforced thermoplastic composite material, of the TWINTEX® type. Again preferably, the closing plate is co-calendered with a non-woven thermoplastic-based carpeting material, to give the rear surface of the seat back a surface finish directly. The closing plate can be flat and include a uniform reinforcement of fibres distributed over its entire surface, but it can also be worked, in a similar manner to the frame body, with areas of whatever shape and/or reinforcing strips placed specifically in areas where greater resistance might be required. 
   The invention also concerns a process for manufacturing an automobile vehicle seat back as defined above, the frame extending over a general plane and featuring functional components, particularly attaching or reinforcing components, with the process being characterized in that:
         the functional components comprising inserts are interconnected by a reinforcing strip, comprising a woven band of mineral and plastic fibres,   the assembly thus formed is placed in a manufacturing supporting frame, attaching the inserts to the support frame in such a way that the reinforcing strip is pulled taut between the various inserts it interconnects,   the assembly is heated,   the heated assembly is placed in an injection mould, where the plastic material is injected such that it overmoulds the strip and, at least partially, the inserts, to form a body for the composite frame.       

   In a preferential arrangement, after demoulding the resulting composite frame, a separately prepared closing plate designed to form the rear surface of the seat back is then fixed to the body by vibration welding. 
   Other characteristics and advantages of the invention will appear in the following description of an automobile vehicle rear seat back frame in accordance with the invention, and of its manufacture. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  depicts a preassembled strip/insert assembly attached to a supporting frame to form part of the seat back frame of the present invention. 
       FIG. 2  depicts a supporting frame of the seat back frame between two heating panels. 
       FIG. 3  depicts the seat back frame with the body of the seat back frame overmoulding the strip and inserts. 
       FIG. 4  depicts the seat back frame with a reinforcing strip interconnecting a plurality of inserts. 
       FIG. 5  depicts an insert that is entirely embedded in an overmoulded plastic material of the seat back frame. 
       FIG. 6  illustrates an insert variant formed a metal wire that is suitably bent to fulfill several functions. 
       FIG. 7  shows another insert variant wherein the metal wire features a section that is bent to form a ring. 
       FIG. 8  shows another insert variant comprising a double insert featuring a wire section and a section formed by a metal plate. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The seat back frame  1  obtained by the process in accordance with the invention essentially comprises, as can be seen in  FIG. 4 , a reinforcing strip  10  comprising a band in TWINTEX® or woven glass fabric, measuring 50 to 70 mm in width for example, that interconnects inserts  20 ,  21 ,  25 ,  26 . Inserts  20 ,  21  and  25  are positioned in each corner of the seat back for example, and feature oblique slits  22  cut in a constituent part in sheet metal, as can be seen more clearly in  FIGS. 5 and 8  for example, or equivalent areas provided on a bent wire illustrated in  FIGS. 6 and 7 , with these slits or equivalent areas being designed to have the reinforcing strip pass through or over them. 
   The lower inserts  20  are designed to act as points for the seat back to pivot on the seat pan. Upper insert  21  acts as a support for a seat back locking device, for example. Insert  25  serves solely as a 90° change-of-direction point for the reinforcing strip. Insert  26  is an additional insert, intended for example to support a safety belt reel, situated on a straight section of strip  10  in the top of the seat back. 
   The ends  11  of the strip are firmly joined together once the strip has been passed through the slits in the various inserts. With this method of assembling the ends of the strip, insert  26 , which features for this specific purpose two parallel slits  27  through which the two ends of the strip are passed while being held one on top of the other, providing a kind of mechanical anchoring that further improves the strength of the joint between the two ends of the strip. 
   The assembly formed by strip  10  and the interconnected inserts  20 ,  21 ,  25 ,  26  is embedded in a body  30  made from a glass-fibre reinforced thermoplastic material, which overmoulds the entire strip and at least part of each insert. 
   A 1-mm thick closing plate  40 , for example, is welded to the rear face of the frame, and can be given a finish covering of carpeting for example. This plate is preferably also made from a material such as TWINTEX® in order to constitute a reinforcing element that helps increase the rigidity of the seat back, and also a sufficiently resistant surface, in particular to act as a floor surface for the vehicle boot if the seat back is folded down, as is known and often demanded. 
     FIG. 4  shows in particular that insert  20 , intended to form an attaching pivot at the bottom of the seat back, features a section that protrudes from the body  30  formed by the overmoulded plastic. Insert  21 , on the other hand, for which the example is shown in greater detail in  FIG. 5 , is entirely embedded in the overmoulded plastic material. Such an insert can feature a cutaway such as the rectangular hole  23 , that can be used to attach other accessories or act as a passageway for other seat back accessories, in which case a matching passageway is also provided in the body  30  and closing plate  40 . 
   Openings  31  can also be provided in the body  30 , with matching cutaways  41  made in the closing plate  40 , to serve as a feedthrough hole for skis or to accommodate an arm-rest, etc. Similarly, other inserts, which may or may not be joined to the strip, could be provided to allow the attachment of other accessories to the seat back, such as a headrest, safety belt reel, or to secure padding material or a lining cover. 
     FIG. 6  illustrates an insert variant, formed in this case by a metal wire  50  suitably bent to fulfill several functions. An oblique section  51  serves as a support and change-of-direction point for the strip  10 . An end section  52  bent back over itself acts as a reinforcement for the overmoulded trunnion. A visible horizontal section  54  serves as an attachment point for the attaching strap of a removable infant seat. Between these various sections the wire can feature intermediate joining areas  55  between which strip  10  can also be passed to increase the strength of the functional sections of the inserts. 
     FIG. 7  shows another variant in which the wire  50  features a section  56  that is bent to form a ring. 
     FIG. 8  shows yet another variant with a double insert featuring a wire section  50  and a section formed by a metal plate  57  provided with a slit  58  through which the reinforcing strip  10  can be passed, and a slit  59  constituting a distortion loop that can deform if subjected to high loads without leading to direct rupture. The wire and the plate act simultaneously as a reinforcement for trunnion  53 . 
   The seat back frame is manufactured as follows: 
   In the first stage, which can be carried out independently of the subsequent stages, the various inserts are stacked such that the slits or areas through which the reinforcing strip passes are aligned so that the strip can be passed through all the inserts at once. The strip  10  is passed through the slits  22 ,  27  of the various inserts or over the adapted oblique sections  51  of the inserts, and its two ends  11  are superimposed and heat-welded together, preferably at an insert such as insert  26 , as indicated earlier. The strip/inserts assembly is then ready for use, and can be stored pending its use in the moulding of the seat back. 
   To produce the seat back, the preassembled strip/inserts assembly is attached to a supporting frame  70  provided with a handling ring as shown in  FIG. 1 . The inserts are held in position on the frame by appropriate fixtures  71 ,  72 , and the strip  10  is tensioned very slightly. 
   The supporting frame  70  is transferred to a heating station, shown in  FIG. 2 , comprising two heating panels  80  between which the supporting frame carrying the reinforcing strip/inserts assembly is placed in order to heat it and permit adequate subsequent overmoulding of the TWINTEX® strip by ensuring partial plastification of the thermoplastic fibres of the strip and raising the temperature of the glass fibres and the inserts. 
   The preheated assembly mounted on the supporting frame is then placed in an injection mould designed for this purpose, with the supporting frame  70  remaining outside the mould. Plastic material reinforced with long glass fibres is injected into the mould and overmoulded on the assembly, which is still held on the supporting frame. 
   The supporting frame bearing the resulting seat back frame comprising the body  30  overmoulding the strip  10  and inserts  20 ,  21 ,  25 ,  26  such as is shown in  FIG. 3 , is used to remove the seat back frame from the mould and transfer it to a workstation where an operator unhooks it from the supporting frame. 
   At a welding station, the closing plate  40  is applied against the body  30  as shown in  FIG. 4  and joined to it by vibration welding. 
   The seat back frame assembly can then be stored for later use. 
   The invention is not limited to the examples and methods of production described above purely as examples. An experienced craftsman could adapt these examples without difficulty by changing the shapes and number of inserts, and the positioning of the reinforcing strip.