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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     The present invention relates to a hinge for wings or doors. 
     In particular, the present invention relates to a hinge which can be used for constraining the doors of electrical appliances, such as ovens, to the respective supporting structures. 
     In the following description and by way of example only, without limiting the scope of the invention, the present invention is described with reference to an oven. 
     Hinges of this type normally consist of two separate parts, kinematically connected to one another, directly or by inserting a lever between them. 
     More precisely, the first of said parts is fixed to the oven structure at one side of the oven mouth, whilst the second part is fixed to one edge of the door, which in that way is rendered movable, with a tilting action, relative to the above-mentioned oven mouth. 
     One or more elastic elements are inserted between the two parts of the hinge. 
     During door rotation starting from its closed position, the elastic elements oppose, during a first step, the detachment of the door from the oven supporting frame and, in a second step, they oppose the subsequent rotation of the door and its consequent lowering to an end of stroke position in which the oven mouth is completely open. 
     In this second opening step, the door, under the combined action of its own weight which promotes its descent and of the elastic elements which apply a braking action, performs a gradual rotation. 
     During door rotation starting from its open end of stroke position, the action of the elastic elements is first balanced by the weight of the door, initially guaranteeing gradual closing rotation; however, then, in the absence of a braking action by the user, the elastic elements push the door towards the oven frame with sufficient force to guarantee its effective closing. 
     Basically, the presence of the hinges with elastic elements balances the door, so that when it is opened it does not drop open, and when it is closed it does not forcefully spring back to its closed position. 
     In its opening and closing movements, irrespective of the action of the user, the door is subject to the action of two different torques, an “opening” torque to which the weight of the door contributes, and a “closing” torque, basically determined by the elastic reaction force of the hinge springs. 
     At least beyond a predetermined door opening angle, for example greater than 30°, the opening torque will advantageously be positive, whilst the closing torque will have a negative value. 
     Said values are the preferred values for good operation of the door. If the spring or springs contained in the hinge were too weak, the opening torque could become negative, requiring that the operator apply a braking action to door opening, otherwise the door would just drop open. In contrast, if the spring or springs were to generate an elastic reaction force that was too great, the closing torque could become positive, therefore resulting in violent door closing. 
     As already indicated, correct door operation basically requires that, at least beyond a predetermined opening angle, the opening torque is positive and the closing torque is negative. 
     The difference in the absolute value between the two torques in practice indicates the versatility of the hinge, that is to say, the range of different door weights that a predetermined hinge can balance. 
     Prior art hinges have the disadvantage of being suitable for balancing doors within a rather limited weight range, therefore obliging manufacturers and users to adopt extensive ranges of hinges in order to be able to vary the weights of the doors. 
     For example, the same electrical appliance, finished with covering surfaces which have different weights, must be fitted with different hinges. This means that in the worst case the hinges and door must be mounted only after the covering has been selected. 
     SUMMARY OF THE INVENTION 
     The aim of the present invention is therefore to increase the balancing capacity of a hinge, so that it can be used with a large number of doors having different weights, without modification of the elastic elements and/or changes to the adjustment or calibration being needed for each door. 
     Accordingly, the present invention provides a hinge for wings or doors comprising the features described in any of the claims herein. 
     The technical features of the present invention, in accordance with the above aim, are clear from the content of the claims herein, in particular claim  1  and, preferably, from any of the claims directly or indirectly dependent on claim  1 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages of the present invention are more apparent in the detailed description which follows, with reference to the accompanying drawings which illustrate a preferred, non-limiting embodiment of the invention, in which: 
         FIG. 1  is a schematic perspective top view of an oven fitted with a door which is constrained to it by two hinges made in accordance with the present invention; 
         FIG. 2  is a schematic side elevation view, with some parts in cross-section or transparent to better illustrate others, of a hinge in accordance with the present invention; 
         FIG. 3  is a perspective view, with an exploded detail, of the hinge of  FIG. 2 ; 
         FIG. 4  is a perspective view of the exploded detail from  FIG. 3 ; 
         FIGS. 5 ,  6  and  7  are respective schematic perspective views of the hinge of the previous figures in three different operating configurations; 
         FIG. 8  is a schematic side elevation view of the hinge of  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , the numeral  1  denotes as a whole an oven comprising a frame  2  to which a door  3  is connected by two hinges  4 , which allow the door to rotate with a tilting action about a first horizontal axis A. 
     With reference to  FIG. 2 , each of the two hinges  4  comprises a first box-shaped element  5  fixed to the oven  1  frame  2 , and a second element  6 , also box-shaped, fixed to the door  3 . The first and second box-shaped elements  5 ,  6  are kinematically connected to one another by a connecting lever  7 . 
     As illustrated in  FIG. 3 , the second box-shaped element  6  has a substantially C-shaped cross-section and extends longitudinally along its own axis B, hereinafter also indicated as the main direction of extension of the second element  6 . 
     The connecting lever  7  comprises a first arm  8 , designed to be rigidly constrained to the first box-shaped element  5 , and a second arm  9  connected to the second box-shaped element  6 . 
     For the connection between the second arm  9  and the second box-shaped element  6 , the hinge  1  comprises a first pin  10  passing through a respective hole made at the end of the second arm  9  and coaxial with the axis A. 
     As illustrated in  FIGS. 2 and 3 , the hinge  4  also comprises a rod  11  and a shaft  12  positioned one after another longitudinally according to the axis B, in the second box-shaped element  6  and hooked to each other. 
     The rod  11  is box-shaped and has a C-shaped cross-section, with a lower end  11   a  pivoting on the lever  7 , at a pin P, in the substantially known way, and an upper end  11   b  which connects to a lower end  12   a  of the shaft  12 . 
     The second box-shaped element  6  houses a first helical spring  13 , fitted on the outside of the shaft  12  and stressed in compression, as described in more detail below. 
     With reference to  FIG. 2 , the second box-shaped element  6  is divided into two portions, an upper portion housing the first spring  13  and a lower portion housing the rod  11 . The two portions, upper and lower, are separated by a separator  14  in which there is a hole  15  for the passage of the shaft  12 . 
     The separator  14  also forms a contact surface for a proximal end coil  13   a  of the spring  13 . 
     The shaft  12  has an upper end  12   b  longitudinally opposite the end  12   a  hooked to the rod  12 . The upper end  12   b  is designed to engage with a distal end coil  13   b  to compress the spring  14 . 
     For the hinge  4 , the spring  13  constitutes an elastic element designed to generate a reaction force which opposes door  3  opening. 
     Only when the closed position is almost reached, from and towards the closed position, overlapping with the above-mentioned elastic action of the spring  13  there is the action of a second pre-compressed helical spring  16 , designed to operate in conjunction with a cam  7   a  made on the rocker lever  7 , through a stem  17  acting on a cam follower  18 , to give the door  3  a spring-to closing movement and to define a door stable semi-open position. 
     The structural and functional features of the second spring  23  have already been described in Italian patent application BO2006A000308 by the same Applicant, to which reference is made, and therefore, said features are not examined in depth in this description. 
     With reference to  FIG. 3 , the C-shaped box-shaped rod  11  comprises a front wall  19  and two lateral walls  20  which are parallel with one another, only one of which is visible in the drawing. In the front wall  19  of the rod  11  there is an opening  21 . A friction element  22 , advantageously made of a plastic material, engages in the opening  21 . 
     With reference to  FIG. 4 , the friction element  22  comprises two teeth  23  and, on opposite sides of them, two respective lateral projections  24   a ,  24   b.    
     The two teeth  23  are designed to hook with a snap-on action on respective contact portions  19   a ,  19   b  formed by the same number of edges of the front wall  19  forming the opening  21 . 
     The lateral projections  24   a ,  24   b  of the friction element  22  are each positioned opposite a respective longitudinal lateral wall  6   a ,  6   b  of the second box-shaped element  6  and, as is more clearly explained below, are designed to engage with the longitudinal walls  6   a ,  6   b  by rubbing. 
     With reference to  FIG. 8 , along the longitudinal walls  6   a ,  6   b  of the second box-shaped element  6  there are respective recesses  25 , opposite one another, the recesses  25  forming a zone  26  for housing the friction element  22 . In said zone the friction element  22  does not apply any friction on the walls  6   a ,  6   b.    
     In the interaction of its projections  24   a ,  24   b  with the longitudinal walls  6   a ,  6   b , the friction element  22  forms respective friction means  27  for the hinge  4 . 
     The teeth  23  of the friction element  22  form removable means  28  for connecting the element  22  to the rod  11 . 
     The following is a brief description of the operation of one of the two hinges  4  starting from the door  3  closed position, schematically illustrated in  FIGS. 2 and 3 . 
     The torque applied to the door  3  when it is opened, by the user and, beyond a predetermined rotation, by the weight of the door  3 , conflicts with the torque generated by the spring  13 , which therefore renders the movement of the door  3  towards the fully open position illustrated in  FIG. 1  gradual and subject to a braking action. 
     Starting from the door  3  fully open position illustrated in  FIG. 1 , a rotation of the door towards the closed position is promoted by the action of the spring  13  and is initially hindered by the weight of the door  3 . 
     In detail,  FIGS. 5 to 7  illustrate in sequence different hinge  4  opening configurations.  FIG. 5  shows a closed configuration,  FIG. 6  a mid-open configuration and  FIG. 7  a substantially open configuration. 
     In passing from the closed configuration of  FIG. 5  to the open configuration of  FIG. 7 , the spring  13  is compressed and loaded by the action applied by the shaft  12  which is in turn pulled by the rod  11 . The rod  11  is pulled by the rotation of the lever  7  relative to the second box-shaped element  6  about the axis A. Therefore, as it pulls the shaft  12 , the rod  11  slides inside the box-shaped element  6  relative to it. 
     In the configuration illustrated in  FIG. 5 , the friction element  22  is positioned in the housing  26  formed by the recesses  25  and, therefore, with its lateral projections  24   a ,  24   b  detached from the longitudinal walls  6   a ,  6   b  of the box-shaped element  6 . In said configuration, since the projections  24   a ,  24   b  are not in contact with the walls  6   a ,  6   b , no friction is applied between the friction element  22  and the second box-shaped element  6 . 
     When the wing or door  3  is opened by the user, that is to say, passing to the configuration illustrated in  FIG. 6 , in which the rod  11  slides towards the axis A, the projections  24   a ,  24   b  exiting the housing zone  26 , begin to engage with the lateral walls of the second box-shaped element  6  by sliding. Said sliding creates friction between the friction element  22  which hinders door  3  opening, also contributing to making the movement fluid and damped and reducing the possibility of sudden, sharp movements by the door. 
     The sliding of the projections  24   a ,  24   b  continues until the hinge  4  fully open configuration is reached, as illustrated in  FIG. 7  and, logically, also in the opposite path which returns the hinge  4  to its closed configuration illustrated in  FIGS. 2 and 3 . 
     In other words, the friction or rubbing created between the friction element  22  and the walls  6   a ,  6   b  of the second element  6  during their relative movement, causes a dissipation of energy, by friction. 
     It was realized that said dissipation, obtained by increasing hinge internal frictions, advantageously allows extension of the door weight range that a predetermined hinge can balance. Experimentally, it was found that a hinge of the type described, when it has no friction element  22 , can balance doors of different weights within a range of approximately 350 g whilst, if the friction element  22  is used, the same hinge can effectively balance doors of different weight within a range of approximately 1000 g. 
     In other words, if the hinge without friction means  27 , consisting for example of the friction element  22 , can balance different doors  3  whose weights differ by a maximum of 350 g, the same hinge when fitted with the friction element  22  can effectively balance different doors  3  whose weights differ by up to 1000 g. 
     Therefore, the friction means  27  increase hinge  3  internal frictions by a value which does not make it difficult to move the door and so they make it possible to adapt the hinge  3  to a vast range of doors, even with weights that are very different to one another. 
     In other words, use of the friction means  27  allows an increase in the absolute value of the difference between the torques for “opening” and “closing” the door  3 , a value which, as already indicated, in practice defines the versatility of the hinge, that is to say, the range of different door weights that a predetermined hinge can balance. 
     Advantageously, the positioning of the friction element  22  in the housing  26 , with its lateral projections  24   a ,  24   b  detached from the longitudinal walls  6   a  and  6   b , means that nothing hinders door  3  closing. Therefore, when the door  3  is closed, the elastic energy of the second spring  16  is not dissipated by the friction means  27  and so can fully contribute to hermetic closing of the door  3 . 
     According to an alternative embodiment of the hinge disclosed, not illustrated, the opposite longitudinal walls  6   a ,  6   b  of the second element  6  are made in such a way that they converge towards the pin  10 , at least over one stretch of their longitudinal extension. In that way, advantageously there is an increase in the friction force developed between the walls  6   a ,  6   b  and the friction element  22  when passing from the door  3  closed position to the open position. 
     The invention described above is susceptible of industrial application and may be modified and adapted in several ways without thereby departing from the scope of the inventive concept. Moreover, all details of the invention may be substituted by technically equivalent elements.

Summary:
A hinge for wings or doors, in particular of electrical appliances, comprises a first element, a second element and a lever for connecting the first and second elements; the lever pivots on the second element and has a first arm integral with the first element to render the first and second elements movable relative to one another with a tilting action between a closed position and an open position; the second element consisting of a substantially box-shaped body containing a spring, inserted between the second element and a second arm of the lever so as to apply an elastic action to the lever.