Abstract:
Process for manufacturing composite material products is disclosed having at least the following operating steps:
       molding at least one plastic material spacer having one or more inserts;   molding at least one composite material product having at least the spacer; and   mechanically working at least one of the inserts for forming at least one threaded hole therein.       
 
     The present invention also relates to the products manufactured with this process.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 371 of PCT/IB2012/050663, filed Feb. 14, 2012, which claims the benefit of Italian Patent Application No. MI2011A000253,filed Feb. 21, 2011, the contents of each of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a process for manufacturing composite material products, in particular shells and roofs for monocoques of motor vehicles. The present invention also relates to the products manufactured with this process. 
     BACKGROUND OF THE INVENTION 
     Known monocoques made of a composite material, in particular carbon fiber, are generally manufactured by fixing to each other by means of adhesives and/or mechanical members, for example bolts, composite material components which are moulded separately. Such known monocoques are characterized both by a high cost, since the whole structure is not intended for the exploitation of the potentialities of the composite material, and by a medium level of repeatability, substantially due to the high use of manual operations within the manufacturing process. As a matter of fact, the monocoques are made of numerous components, all moulded separately by means of a manual stratification, which are then assembled manually or by means of gluing templates. The components are therefore first produced and subsequently assembled, by following the classic production and assembly process typical of the motor vehicle industry. The components are generally obtained by means of moulding processes with fiber carbon substrates pre-impregnated with resin, known as pre-preg, which are layered manually and cured in an autoclave. This process requires long manual workings and expensive materials, furthermore it does not ensure as repeatability comparable with all the other parts of the vehicle. The monocoques produced until now are therefore also not much suitable for the mass production. The manufacturing processes further require very articulated systems which lead, in most cases, to have tens of moulds reserved for producing a single component. Moreover, the products must be disadvantageously worked within few days since the material highly degrades if left at room temperature before the cure cycle, so that such known process can hardly thee sudden production stops and involves a high risk of producing rejects. 
     The known monocoques are therefore very expensive and difficult to produce in a high mass due to the high number of few repeatable components. The parts are mainly made up of pre-impregnated fibers, which are expensive and require a high deftness. Their manufacturing process is further characterized by a clear separation between production and assembly, the used moulds have a limited life and the production cycle in which they are used provides for the use of a lot of moulds in view of a single manufactured piece. 
     U.S. Pat. No. 5,079,055 discloses a reinforcement member for composite material products, which member is provided with an insert with a threaded hole. However, during the moulding of the composite material with the reinforcement member, such threaded hole may be disadvantageously filled with resin, since it is open to the outside. 
     In order to solve this disadvantage, FR 2783196 discloses a spacer provided with an insert with a threaded hole which is closed by one or more plugs. A plug is removed with a mechanical working after the moulding of the composite material. However, this known process is more expensive, since it requires the application and the removal of the plugs from the threaded hole, and further it does not allow a precise arrangement of the threaded hole with respect to the moulded product if the relative position of the inserts with respect to the product is not perfect. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a process and products which are free from said disadvantages. Said object is achieved with a process and a product, whose main features are disclosed in claims  1  and  13 , respectively, while other features are disclosed in the remaining claims. 
     The process and the system according to the present invention allow not only to pull down the costs, thereby allowing the use of composite material products on a mass production volume, but also to ensure the repeatability required by the production standards. 
     The process includes a co-curing step, in which at least two components are produced so that a main component acts as a mould for a secondary component. Both components are then cured together by means of intermediate substrates, thus avoiding gluing steps. This process can be obtained by means of a particular modular system which assumes different functions during the production process. 
     The intermediate substrates further allow to compensate tolerances, if any, between the components, so that the final product has precise shapes and sizes. For this purpose, the main component is preferably moulded between two main moulds with an RTM process, so that both its inner wall and its outer wall have surfaces with precise shapes and sizes. 
     The present invention also relates to a monocoque comprising a shell which substantially corresponds to the compartment of a motor vehicle and a roof which covers this shell. These two components are preferably manufactured by means of the process and the system according to the present invention. The costs of the process are relatively low thanks to the massive use of production techniques differing from the pre-preg in autoclave, such as the RTM (Resin Transfer Moulding) and braiding processes. Both these processes are based on the laying of dry fibers inside moulds and on the subsequent injection of resin. The braiding process is based on the automatic weaving of the fibers on a mandrel and on the subsequent injection of resin, while the RTM process is based on the deposition of dry fabrics and the subsequent injection of resin. The shaping of the substrates and their subsequent deposition in the moulds can be automated, thus making more repeatable and economic the parts produced with these processes. 
     The modularity of the moulds involves a reduction not only of the number of moulds but also of the number of moulds per number of pieces: some monocoques produced until now, for example, are produced in a single moulding step. The complexity of the geometries and the number of subsets requires several tenths of moulds for manufacturing a single component. In the process and the system according to the invention, however, there is the opposite situation, in which few moulds produce a high number of parts, exactly thanks the modularity of the system. 
     A further advantage of the process and the system consists of the combination of the modular moulds, in which the produced parts become a mould for the subsequent ones, and of the massive use of processes less aggressive than the pre-preg, which leads to a life of the moulds expected in 400 pieces for the main moulds and 800 pieces for the secondary moulds, in view of a life of about 150 pieces of the traditional moulds used until now. 
     The reduction of the equipments costs, thus, involves not only a reduction of the moulds number, but also lower maintenance and regeneration connected to the moulds during their use. 
     Another advantage of the process and the system consists of the possibility of carrying out several production steps in parallel. The monocoques produced until now in few very complex moulding steps are very exposed to the risk of rejects. A single complex item is certainly more subject to errors and defects than another one made up of higher number of simple and especially unlinked steps. Various stops carried out in parallel allow to handle both possible remakings of some components and possible stops of the production. 
     Particular spacers allow both to increase the moment of inertia of the resistant sections of the monocoque, thus conferring a high structural rigidity to the latter, and to obtain space for housing metal inserts fur the structural connection with other parts of a motor vehicle. These spacers are preferably arranged between substrates belonging to different sections of the monocoque but they can also be arranged in the middle of the stratification of some components. 
     The process is advantageously simplified by moulding the inserts in given positions in the spacers, so that these inserts are not moulded between two substrates of the composite material components, thus decreasing the complexity of the working of the substrates. Furthermore, the inserts are worked, for example with threaded holes, at the end of the production process, so as to simplify this process and obtain also a final product worked with precision, since the position of the threaded holes does not depend on the position of the inserts but is determined by taking as an absolute reference the position of the final product. Thus, with this arrangement, possible imprecise arrangements of the inserts in the final product are compensated. 
     The main component, namely the inner wall of the monocoque shell, is preferably produced with an RTM process, in particular the RTM process according to the Italian patent application MI2010A001072, by means of some main moulds, and houses, in the middle of its stratification, seven spacers preferably provided with metal inserts which are housed inside auxiliary moulds filled with epoxy foam which is cured to assume the final shape of the spacer. These inserts may also include elements made of a composite material, in particular carbon fiber. 
     Particular spacers to be arranged between the main component and the secondary components, namely between the inner and outer walls of the monocoque shell, can be produced in parallel always with the same process, namely by creating hollow composite material structures which contain the inserts and which are left empty or are filled with epoxy foam. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and features of the process, the spacer and the products according to the present invention will become apparent to those skilled in the art from the following detailed and non-limiting description of an embodiment thereof with reference to the accompanying drawings in which: 
         FIG. 1  shows an enlarged section of the auxiliary moulds in a first step of the process; 
         FIG. 2  shows an enlarged section of the auxiliary moulds of  FIG. 1  in a second step of the process; 
         FIG. 3  shows a spacer obtained by means of the auxiliary moulds of  FIG. 1 ; 
         FIG. 4  shows a perspective view of the main moulds in a third step of the process; 
         FIG. 5  shows a perspective view of the main moulds of  FIG. 4  in a fourth step of the process; 
         FIG. 6  shows an enlarged and partial section of the main moulds of  FIG. 5 ; 
         FIG. 7  shows the section of  FIG. 6  in a fifth step of the process; 
         FIG. 8  shows a perspective view of the main moulds of  FIG. 4  in the filth step of the process; 
         FIGS. 9 to 12  show perspective views of the secondary moulds in a sixth step of the process; 
         FIGS. 13 to 16  show perspective views of the secondary moulds of  FIGS. 9 to 12  in a seventh step of the process; 
         FIG. 17  shows a perspective view of the moulds and of the components in an eighth step of the process; 
         FIG. 18  shows a perspective view of the moulds in a ninth step of the process; 
         FIG. 19  shows a enlarged and partial section of the moulds of  FIG. 18 ; 
         FIG. 20  shows the section of  FIG. 19  in a tenth step of the process; 
         FIG. 21  shows a perspective view of a shell manufactured by means of the process; 
         FIG. 22  shows a top view of the shell of  FIG. 21 ; 
         FIG. 23  shows section XXIII-XXIII of  FIG. 22 ; 
         FIG. 24  shows detail XXIV of  FIG. 23 ; 
         FIG. 25  shows section XXV-XXV of  FIG. 22 ; 
         FIG. 26  shows detail XXVI of  FIG. 25 ; 
         FIG. 27  shows a perspective view of a roof manufactured by means of the process; and 
         FIG. 28  shows a monocoque comprising the shell of  FIG. 21  and the roof of  FIG. 27 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , it is seen that in a first step of the process one or more first inserts  1 ,  2  are arranged in one or more auxiliary moulds  3 ,  4 , in particular in contact with at least one functional surface of these moulds. The first inserts  1 ,  2  are preferably made of metal, particularly aluminum or light alloy, of a composite material, in particular carbon fiber, or of a combination of these materials, for example by moulding in a preliminary step a metal insert between two or more substrates of fibers. The auxiliary moulds  3 ,  4  are preferably made of a composite material, in particular carbon fiber. The auxiliary moulds  3  and/or  4  are preferably provided with protrusions  5  and/or seats  6  to maintain the first inserts  1 ,  2  in a given position. To this end, the first inserts  1 ,  2  have shapes complementary with said protrusions  5  and/or seats  6 . In particular, protrusions  5  are pins adapted to be inserted into corresponding holes formed in a first insert  1 , preferably with a coupling with friction, so that insert  1  remains in position even if the auxiliary moulds  3 ,  4  are reversed. Also insert  2  can be arranged in seat  6  with a coupling with friction. 
     Referring to  FIG. 2 , it is seen that in a second step of the process, plastic material  7  is injected through inlets and outlets  8  into the auxiliary moulds  3 ,  4 , after which it is cured by heating the auxiliary moulds  3 ,  4  in a oven at a temperature between 80° C. and 150° C. The auxiliary moulds  3 ,  4  are preferably rotated during their heating to evenly distribute the plastic material  7  in them. The plastic material  7  is preferably a material, in particular epoxy foam, which expands during the cure. 
     Referring to  FIG. 3 , it is seen that, alter the epoxy foam has cured, the auxiliary moulds  3 ,  4  are cooled to a temperature below 50° C., opened and separated from product  7 , which forms in particular a first spacer for composite material products. Spacer  7  comprises thus the cured epoxy foam which incorporates at least partially the first inserts  1 ,  2 , which may protrude from the first spacer  7  or have a surface visible outside of the first spacer  7 . Holes  9  of insert  1  for pins  5  are then open to the outside. 
     Referring to  FIGS. 4 to 6 , it is seen that in a third step of the process one or more, in particular two first main substrates  10  of fibers, in particular carbon fibers, preferably dry, namely coupled with a quantity of resin from 0 to 10%, preferably 5%, by weight, are arranged on at least one functional surface of a first main mould  11 . One or more first spacers, in particular one or more first spacers  7  with one or more first inserts  1 ,  2  manufactured as described above, can be arranged in contact with the first main substrates  10  and/or with the first main mould  11 , One or more, in particular two second main substrates  12  of fibers, in particular carbon fibers, preferably dry, are then arranged on the first main substrates  10  and/or on the first main mould  11  and/or on the first spacers  7 . At least one portion of the first spacers  7  is preferably arranged between the first main substrates  10  and the second main substrates  12 . At least one second main mould  13  is aligned with the first main mould  11 , for example by means of complementary pins and holes, and is fastened to the first main mould  11 , for example by means of mechanical fastening devices, in particular toggle latches and/or screws, so that the first main substrates  10 , the first spacers  7  and the second main substrates  12  are arranged between the functional surfaces of the main moulds  11 ,  13 . The main moulds, in particular the second main mould  13 , can be provided with movable walls  14  and/or blocks  15  to form undercut portions and/or deep cavities, respectively, in a moulded product. In  FIG. 4  the main substrates  10 ,  12  are shown for simplicity with a rectangular shape, however each main substrate  10 ,  12  can be divided into a plurality of portions having different shapes, sizes, thicknesses and/or wefts, which portions are preferably cut by numerical control machines. Also the first spacers  7  may have shapes and/or dimensions differing from those shown in  FIG. 4 . 
     In a fourth operating step of the process, resin  16  for composite materials is injected at a pressure between 0.5 bar and 3.5 bar, in particular between 1.5 and 2.5 bar, through one or more inlets  17  between the main moulds  11 ,  13 , preferably evacuated to a pressure lower than 0.5 bar, in particular comprised between 0.001 and 0.02 bar, through one or more outlets, so as to impregnate the main substrates  10 ,  12  with resin  16 . Resin  16  is then cured by heating the main moulds  11 ,  13  in an oven to mould at least one main component. The main moulds  11  and/or  13  are preferably heated, in particular at a temperature comprised between 25° C. and 70° C., before injecting resin  16  in them. The main moulds  11  and/or  13  are preferably made of a composite material, in particular they are made up by a plurality of substrates of fibers, in particular carbon fibers, pre-impregnated with a resin which is cured in a preliminary step to achieve the finished moulds  11  and/or  13 . The first main mould  11  has a mainly convex functional surface, while the second main mould  13  has a mainly concave functional surface. In particular, the first main mould  11  has a functional surface with two convex portions separated by a concave canal, while the second main mould  13  has a functional surface with two concave portions separated by a convex canal. The cross sections of the convex portions and/or of the concave canal of the first main mould  11  and/or of the concave portions and/or of the convex canal of the second main mould  13  are substantially rectangular or substantially trapezoidal. 
     Referring to  FIGS. 7 and 8 , it is seen that in a fifth step of the process the main moulds  11 ,  13  are cooled, opened at a temperature between 40° C. and 70° C., then separated from the main component  18  comprising the main substrates which are cured with resin  16  to form at least one inner wall  10  and/or one outer wall  12 , respectively, of the main component  18  with at least one first spacer  7  arranged between these walls  10 ,  12 . In an alternative step of the process, the main component  18  remains on the first main mould  11 , so that the inner wall  10  remains in contact with the functional surface of the first main mould  11 . 
     Referring to  FIGS. 9 to 12 , it is seen that in a sixth step of the process, which can carried out before, during or after the previous steps, one or more, in particular two secondary substrates  19 ,  20 ,  21 ,  22  of fibers, in particular carbon fibers, preferably pre-impregnated (pre-preg), namely coupled with a quantity of resin higher than 10% by weight, are arranged on at least one functional surface of at least one first secondary mould  23 , of at least one second secondary mould  24 , of at least one third secondary mould  25  and of at least one fourth secondary mould  26 , respectively. One or more second inserts  27 ,  28 ,  29 ,  30 , preferably of metal, in particular plates made of aluminum or light alloy, and/or of a composite material, can be arranged between two secondary substrates or between a secondary substrate and a secondary mould or outside of the secondary substrates, which are then arranged between a second insert and a secondary mould. In  FIGS. 9 and 12  the second inserts  27 ,  30  are arranged between the two secondary substrates  19  or  22 , respectively, while in  FIGS. 10 and 11  the second inserts  28 ,  29  are arranged between the secondary substrates  20 ,  21  and the second secondary mould  24  or the third secondary mould  25 , respectively. In  FIGS. 9 to 12  the secondary substrates  19 ,  20 ,  21 ,  22  are shown for simplicity with a rectangular shape, however each secondary substrate  19 ,  20 ,  21 ,  22  can be divided into a plurality of portions having different shapes, sizes, thicknesses and/or wefts. Also the second inserts  27 ,  28 ,  29 ,  30  may have shapes and/or dimensions differing from those shown in  FIGS. 9 to 12 . 
     The secondary moulds  23 ,  24 ,  25 ,  26  with the secondary substrates  19 ,  20 ,  21 ,  22  and the second inserts  27   28 ,  29 ,  30  are inserted into vacuum bags, heated to a temperature higher than 120° C. and arranged in an autoclave at a pressure higher than 5 bar, so that the secondary substrates  19 ,  20 ,  21 ,  22  and the second inserts  27 ,  28 ,  29 ,  30  are pressed on the secondary moulds  23 ,  24 ,  25 ,  26  while the resin of the secondary substrates  19 ,  20 ,  21 ,  22  is cured. 
     Referring to  FIGS. 13 to 16 , it is seen that in a seventh step of the process the secondary substrates  19 ,  20 ,  21 ,  22 , after the resin has cured, form secondary components  19 ,  20 ,  21 ,  22  having at least one surface corresponding to at least one functional surface of the secondary moulds  23 ,  24 ,  25 ,  26 . The secondary components  19 ,  20 ,  21 ,  22  can be separated from the secondary moulds  23 ,  24 ,  25 ,  26  or left on them. The secondary moulds  23 ,  24 ,  25 ,  26  have a mainly concave functional surface. 
     Referring to  FIG. 17 , it is seen that in an eighth step of the process the main component  18  is arranged on at least one further first main mould  31  having at least one functional surface substantially equal to a functional surface of the first main mould  11 , or, alternatively, the main component  18  is left on the first main mould  11 . One or more, in particular three seconds spacers  32 ,  33 ,  34 , preferably covered by at least one adhesive layer, are arranged on the main component  18 . At least one adhesive layer is preferably applied on the portions of the main component  18  not covered by the second spacers  32 ,  33 ,  34 , after which one or more, in particular two intermediate substrates (not shown in the figure) of fibers, in particular carbon fibers, pre-impregnated with a resin (pre-preg), are arranged on the second spacers  32 ,  33 ,  34  and/or on the main component  18  arranged on the first main mould  11  or  31 . 
     During the deposition of the intermediate substrates on the main component  18  and/or on the second spacers  32 ,  33 ,  34 , the intermediate substrates can be covered by at least one anti-adhesive sheet and the secondary components  19 ,  20 ,  21 ,  22  can be placed temporarily on the intermediate substrates to verify the correct position of the second spacers  32 ,  33 ,  34 , preferably by arranging the secondary moulds  23 ,  24 ,  25 ,  26  on the secondary components  19 ,  20 ,  21 ,  22 , after which the secondary components  19 ,  20 ,  21 ,  22  and the anti-adhesive sheet are removed. 
     The intermediate substrates are then pressed on the main component  18  by means of a vacuum bag, after which at least one adhesive layer is preferably arranged on the intermediate substrates. The secondary components  19 ,  20 ,  21 ,  22  are then arranged on the intermediate substrates and/or on the second spacers  32 ,  33 ,  34  and/or on the main component  18  by means of further secondary moulds  35 ,  36 ,  37 ,  38  that have at least one functional surface substantially equal to a functional surface of the secondary moulds  23 ,  24 ,  25 ,  26 , respectively. As an alternative to the further secondary moulds  35 ,  36 ,  37 ,  38 , the secondary components  19 ,  20 ,  21 ,  22  are left on the secondary moulds  23 ,  24 ,  25 ,  26 . 
     The main moulds  11 ,  13  and/or  31  and the secondary moulds  23 ,  24 ,  25 ,  26  and/or  35 ,  36 ,  37 ,  38  are suitably provided with surfaces with shapes and/or elements, for example pins and holes, for carrying out a mechanical coupling with corresponding shapes and/or elements, for example holes and pins, of at least one main mould  11 ,  13 ,  31 , and/or of at least one secondary mould  23 ,  24 ,  25 ,  26 ,  35 ,  36 ,  37 ,  38  and/or of at least one further secondary mould  39  having a functional surface substantially equal to at least one portion of a functional surface of the second main mould  13 . 
     Referring to  FIG. 18 , it is seen that in a ninth step of the process the first main moulds  11  and/or  31  and the secondary moulds  23 ,  24 ,  25 ,  26 ,  35 ,  36 ,  37 ,  38  and/or  39  are fastened to each other with mechanical fastening devices, in particular toggle latches and/or screws, to form a modular moulding assembly  40 . The first main moulds  11  and/or  31  are preferably mounted on a carriage (not shown in the figure) which is equipped with a locking system which allows a mutual movement between mould and carriage, so as to be able to easily move the moulding assembly  40 . 
     Referring to  FIG. 19 , it is seen that the main component  18  and the secondary component  20  provided with the second insert  28  are arranged between a first main mould, for example the further first main mould  31 , and a secondary mould, for example the further second secondary mould  36 . The second spacer  33  is arranged between the main component  18  and the secondary component  20 , while the intermediate substrates  41  are arranged between the second spacer  33  and the secondary component  20 . The second spacers  32 ,  33  and/or  34  are preferably made of a composite material, in particular carbon fiber preferably dry, and are moulded by means of an RTM or braiding process in a preliminary step so as to form a hollow body  42  having a cavity  43  which can be left empty or filled with plastic material, in particular epoxy foam. The moulding assembly  40  is then heated, in particular in an oven to at least 130° C. and/or for at least 3 hours, so as to cure the resin of the intermediate substrates  41 , which form after the cure a single body with the main component  18 , with the secondary components  19 ,  20 ,  21 ,  22  and/or with the second spacers  32 ,  33 ,  34 . During the cure of the resin of the intermediate substrates  41  in the moulding assembly  40 , a further main component can be moulded by means of the main moulds  11 ,  13  and/or one or more further secondary components can be moulded by means of the secondary moulds  23 ,  24 ,  25 ,  26 . 
     Referring to  FIG. 20 , it is seen that in a tenth step of the process the moulding assembly  40  is opened and the final product  44  comprising the main component  18  joined to the secondary components  19 ,  20 ,  21 ,  22  by means of the cured intermediate substrates  41 , is separated from the main mould  31  and from the secondary moulds  35 ,  36 ,  37 ,  38 ,  39 . The final product  44  is then placed on a support and worked mechanically, preferably by numerical control tools on five axes, to form threaded holes  45  and/or non-threaded holes  46  and/or recesses  47  and/or openings in the final product  44  and in particular in the inserts included in the final product  44 , for example in the first insert  1  and in the second insert  28 , so as to fasten elements and/or structures to the final product  44 . The metal inserts having at least one surface facing outwards, such as the second insert  28 , can also be refaced to obtain reference surfaces with precise dimensions and positions. 
     Referring to  FIGS. 21 to 26 , it is seen that a shell  48  of a monocoque can comprise said final product  44 , namely it can be made by means of the process and/or the moulds according to the present invention. Shell  48  is then provided with at least one inner structure comprising the main component  18 , which inner structure is joined to an outer structure comprising the secondary components  19 ,  20 ,  21 ,  22 . The lower side portions of shell  48 , corresponding to the door sills of the monocoque, comprise the second spacers  32 ,  34 , which preferably have a substantially tubular shape and/or are hollow and/or are made with the braiding technique. At least one insert  49  can be arranged in the second spacers  32 ,  34 . The lower rear portion of shell  48 , corresponding to the bench behind the seats in the monocoque, comprises the second spacer  33 , which is preferably hollow and/or made with an RTM process. The upper front portion of shell  48 , corresponding to the base of the windscreen of the monocoque, comprises at least one pair of substantially wedge-shaped cavities  50 ,  51 , which are obtained by means of blocks  15  of the second main mould  13 . 
     Referring to  FIGS. 27 and 28 , it is seen that a roof  52  of a monocoque can comprise said final product  44 , namely it can be made by means of the process and/or the moulds according to the present invention. Roof  52  has at least one pair of projections  53 ,  54  which protrude downwardly below the frame for a windshield and have a shape substantially complementary to the shape of cavities  50 ,  51 , namely substantially wedge-shaped, so that in a final assembly step roof  52  can be fixed on shell  48  by fixing projections  53 ,  54  in cavities  50 ,  51 , preferably by means of adhesive substances, to form a monocoque  55 . Roof  52  may be fixed to shell  48  also by means of mechanical fastening elements. 
     Any variants and/or additions may be made by those skilled in the art to the embodiment of the invention described and illustrated herein while remaining within the scope of the following claims. In particular, further embodiments of the invention may comprise the technical features of one of the following claims with the addition of one or more technical features, taken individually or in any mutual combination, described in the text and/or illustrated in the drawings.