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TECHNICAL FIELD 
     The present invention relates to a spacing/levelling device for laying slab-shaped products, such as tiles and the like, for cladding surfaces. 
     PRIOR ART 
     In the sector of laying tiles for cladding surfaces, such as floorings, walls and the like, the use of spacer devices is known, which, as well as spacing the tiles, enable them also to be laid in planar fashion. These devices are commonly known as spacing/levelling devices. 
     Spacing/levelling devices of known type generally comprise a base, positionable below the laying surface of at least two adjacent tiles, from which at least a separator element projects which is destined to contact, with its lateral flanks, the facing sides of the two tiles to be arranged adjacent on the laying surface. 
     The spacing/levelling device is also provided with presser means which press the in-view surfaces of the products towards the base in such a way as to level them, cooperating with the portion of the separator element which emerge above the plane defined by the in-view surface of the tiles. 
     Although these spacing/levelling devices are particularly effective in their tile-levelling action, they however have the drawback of not being applicable at the corners of the slab products, i.e. where a greater precision is necessary in the carrying-out of the alignment along the flanking direction of the products and also in the laying thereof, such as to prevent the surface from being irregular. 
     Also known for the squared arrangement of the tiles, between the corners of the tiles, is the use of other types of spacing devices, or cross spacers, which, though particularly effective for the equidistant and regular flanking of the tiles, do not however perform any levelling function; another alternative is the expert eye of the technical expert when laying. 
     There is, therefore, in any case the need to use more than one type (for example up to three different types) of spacing/levelling devices or non-levelling devices according to whether it is necessary to act on the lateral edges of the tile or the corners thereof. 
     This spacing devices are differentiated, for example, by the arrangement of the elements projecting from the base which separates the tiles; in particular three different types of spacer are known, a first of which exhibits a cross-conformation in plan view, a second of which is T-shaped and a third of which is simply straight, such that they can be respectively used in different zones of the tile, as is more clearly visible in  FIGS. 1   a ,  1   b  and  1   c , in which three different possible known tile-laying schemes are known. 
     Examples of levelling spacers of known type are described in documents nos. BE 815 222 and WO 2008/118418. 
     An aim of the present invention is to obviate the above-mentioned drawbacks in the prior art, with a solution that is simple, rational and relatively economical. 
     These aims are attained by the characteristics or the invention as reported in the independent claim. The dependent claims delineate preferred and/or especially advantageous aspects of the invention. 
     DESCRIPTION OF THE INVENTION 
     In particular, the invention discloses a spacing/levelling device for laying slab-formed products for cladding surfaces that comprises a base, positionable below the laying surface of at least two adjacent and flanked slab products with respect to a flanking direction, from which at least a separating element projects, suitable for contacting at least a portion of the facing flanks of the two slabs, and presser means associated to the separator element suitable for pressing the in-view surfaces of the slab products such as to level them, characterised in that it comprises at least a corner spacer which projects from the base with respect to the separating element and is suitable for coming into contact with the flanks that are perpendicular to the facing flanks of the slab products for aligning thereof along a perpendicular direction to the flanking direction, the corner spacer being mobile between a raised position, in which it projects superiorly of the base, and a non-interfering position with the perpendicular flanks of the products, or a lowered position; for example, in the non-interfering position the area of the corner spacer is at least partially contained within the area of the base. 
     Thanks to this solution, the spacing/levelling element can be used both at the lateral edges of two slab products to be flanked and at the corners of the products to be arranged squared, independently of the laying scheme of the products, while at the same time having a levelling function for the products laid and a distancing function for between the products themselves. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further characteristics and advantages of the invention will emerge from a reading of the following description provided by way of non-limiting example, with the aid of the figures illustrated in the accompanying figures of the drawings. 
         FIG. 1  is an axonometric view of a surface covered with tiles by means of the spacing/levelling device according to the device. 
         FIG. 1   a  is a schematic plan view of a first possible laying scheme of slab products in a shoulder-to-shoulder arrangement; 
         FIG. 1   b  is a schematic plan view of a second possible laying scheme of slab products in a staggered arrangement; 
         FIG. 1   c  is a schematic plan view of a third possible laying scheme of slab products in a complex arrangement; 
         FIG. 2  is a plan view of a detail of  FIG. 1 ; 
         FIG. 3  is the view along section line III-III of  FIG. 2 ; 
         FIG. 4  is a view along section line IV-IV of  FIG. 2 ; 
         FIG. 5  is a plan view of a further detail of  FIG. 1 ; 
         FIG. 6  is a lateral view of a first variant of a first embodiment of the spacing/levelling device according to the invention; 
         FIG. 7  is an axonometric view from above of  FIG. 6 ; 
         FIG. 8  is a lateral view of a second variant of the first embodiment of the spacing/levelling device of the invention; 
         FIG. 9  is an axonometric view from above of  FIG. 8 ; 
         FIG. 10  is a lateral view of a third variant of the first embodiment of the spacing/levelling device of the invention; 
         FIG. 11  is an axonometric view from above of  FIG. 10 ; 
         FIG. 12  is a lateral view of a second embodiment of the spacing/levelling device according to the invention; 
         FIG. 13  is an axonometric view from above of  FIG. 12 ; 
         FIG. 14  is a plan view of  FIG. 13 . 
         FIG. 15  is an axonometric view from above of a third embodiment of the spacing/levelling device according to the invention. 
         FIG. 16  is a lateral view of  FIG. 15 . 
         FIG. 17  is a frontal view of  FIG. 15 . 
         FIG. 18  is cross-section XVIII-XVIII of  FIG. 17 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With particular reference to the figures of the drawings,  10  denotes in its entirety a spacing/levelling device suitable for facilitating laying of slab products, such as tiles and the like, denoted in their entirety with the letter P, and destined to clad surfaces, i.e. floorings, walls and the like. 
     The device  10  comprises a base  20  having a broad shape, for example polygonal, circular or an irregular shape defining a lower surface  21 , for example flat, suitable for being resting on a layer of adhesive arranged on the floor surfaces which is destined to be covered by the tiles P. 
     The upper surface  22  of the base  20  is, differently, suitable for restingly receiving a portion of the laying surface of one or more tiles P. 
     In practice, the base  20  is positioned below at least two (or more) adjacent tiles, as will more fully emerge in the following. 
     A separator element  30  emerges from the base  20 , which separator element  30  is destined in use to contact at least a portion of the facing flanks of at least two tiles P to be flanked along a flanking direction indicated with letter A in the figures. 
     The separator element  30  is a slab-shaped parallelepiped body, for example having a rectangular base which defines a slim separating wall developing in a perpendicular direction with respect to the base and destined to separate the two flanked tiles P by a distance that is equal to its thickness. 
     In particular, the separator element  30  comprises two lateral flanks  31  parallel to one another. 
     Further, the separator element  30 , in the embodiment shown in the figures, exhibits a greater height than the thickness of the tiles P to be laid, such that the top of the separator element, once the tiles P are resting on the upper surface  22  of the base  20 , projects superiorly (by a good amount) above the plane to be leveled defined by the laying surface of the tiles P. 
     Further, the separator element  30  is provided with a window  32  passing from side to side in a transversal direction, the upper edge  33  of which is destined to be located superiorly of the level of the in-view surface of the tiles P to be leveled and the lower edge  34  of which is destined to be laid inferiorly of the level (for example coinciding with the base  20 ). 
     Further, the separator element  30  exhibits a line or section having a pre-determined break  35  which in use will be arranged inferiorly at the level of the in-view surface of the tiles to be spaced and leveled, for example at the same level as or at a lower level than the upper surface  22  of the base  20 . 
     Thanks to this pre-determined break line or section  35 , the emerging portion of the device  10  can be easily removed, once the tiles P have been laid and the adhesive supporting them has solidified. 
     The device  10  further comprises presser means associated to the separating element  30  and suitable for pressing the in-view surfaces of the tiles P towards the base  20 , such as to level the tiles. 
     In particular, the presser means comprise a wedge element  40  (visible for the sake of simplicity only in  FIGS. 2 and 3 ) provided with a lower surface  41  that is flat and suitable for being arranged in use parallel to the base  20  and an upper surface  42  that is inclined and provided with abutting elements, such as small teeth  43  or knurling (visible in  FIG. 3 , where the wedge element  40  has been drawn schematically in a broken line). 
     The wedge element  40  can be inserted internally of the window  32  such as to slide, with the lower surface  41  resting on the in-view surfaces of the tiles P, such that the upper surface  42  thereof goes into contact with the upper edge  33  of the window  32 —for example such that the teeth  43  engage the upper edge—and the wedge element  40  is thus pressed against the tile P and pushes the tiles towards the base  20 . 
     The separating element  30  exhibits a reinforcement, for example a zone having an increased section, located superiorly to the window  32  and able to prevent, in use, flexion of the separating element when the wedge  40  is forced into the window  32 . It is however not excluded that the presser means can alternatively comprise a block destined to slide along the separator element and provided with teeth suitable for engaging a rack associated to the separator element or another system of known type suitable for imparting a gradual and substantially uniform pressure on the in-view surface of the two or more flanked tiles P to be leveled. 
     In particular, for the aims of the present invention, the device  10  comprises at least a corner spacer  50  which projects from the base  20 , squared with the separator element  30 . 
     In practice, in plan view the separator element  30  and the corner spacer  50  are arranged in a cross. 
     The corner spacer  50  is destined to go into contact with the perpendicular flanks to the facing flanks of the tiles P in order to align the perpendicular flanks along a direction D that is perpendicular to the flanking direction A. 
     The corner spacer  50  is, advantageously, mobile between a raised position, in which it projects superiorly to the base  20  and is raised with respect thereto and a non-interfering position with the perpendicular flanks of the tiles P (with respect to direction D). 
     In practice, the corner spacer  50  can be configured such that in the non-interfering configuration thereof it lowers such that its vertical dimension is contained totally or partially in the vertical dimension (thickness) of the base  20 . 
     In the example, the corner spacer  50  comprises at least a block  51  provided with two lateral flanks  52 , which, when the block  51  is in the raised position, will come into contact with the flanks of two tiles P to be flanked along the direction D. 
     In the preferred embodiment illustrated in the figures, the block  51  is associated to the base  20  in such a way that in the non-interfering position the lateral flanks  52  are all contained within the vertical dimension of the base  20 , i.e. the block  51  is hidden in the base  20 , and in the raised position emerge superiorly to the base such that they can function as abutting elements for the flanks of the tiles P to be arranged squared. 
     The thickness in plan view of the corner spacer  50  is advantageously substantially equal to the plan thickness of the separator element  30 , such that the tiles P are distanced both along direction D and along flanking direction A by a same distance. 
     It is however possible that the thickness in plan view of the corner spacer  50  is different to the thickness in plan view of the separator element  30  according to the different laying requirements of the tiles P. 
     In the illustrated examples, the device  10  comprises, in the example, at least two corner spacers  50 , as described above and independent of one another, which are arranged on the opposite sides with respect to the separator element  30 . 
     The lateral flanks  52  of the two corner spacers  50  are two-by-two substantially coplanar and perpendicular to the lateral flanks  31  of the separator element  30 , such as to guarantee the effective alignment of the flanks of the tiles P along direction D. 
     It is however possible that the device  10  might alternatively comprise a single corner spacer  50  which crosses the separator element  30  (for example through the window  32 ). 
     In a preferred embodiment shown in  FIGS. 6-11 , the block  51  is realised in at least a plastically or elastically yielding material and develops projectingly from the base  20 . 
     In practice, each block  51  exhibits a free end with the opposite end fixed to the base  20  and is realised in a single piece with the base. 
     Thanks to the yielding nature of the material the block  51  is made of, it is arranged folded upwards by an acute angle in its raised position, while it is arranged substantially coplanar with the base  20  in its non-interfering or lowered position.  FIGS. 6-7 ,  8 - 9  and  10 - 11  show three respective variants in the preferred embodiment which differ in the shape and arrangement of the corner spacers  50 . In an alternative embodiment, shown in  FIGS. 12-14 , the block  51  (which can also be made of a rigid material) is slidably associated, telescopically, to the base  20  and is provided with easy-break predetermined-fracture ribs  53  destined to temporarily retain the block  51 , and therefore the lateral flanks  52  thereof, in the raised position. 
     In practice, the base exhibits two through-slots  23  in which the blocks  51  can slide substantially snugly; the predetermined fracture ribs  50  are defined on the upper edge of each slot  23  and on the lower edge of the blocks  51 . In this way, in the raised position the block  51  is maintained at a higher level than the base  20  by the predetermined fracture ribs  53 , while once the ribs are broken the block  51  can slide internally of the slot  23  and lower to below the level of the base. 
     Lastly, in a preferred embodiment shown in figures from  15  to  18 , the base  20  exhibits at least a lateral edge  24  inclined by an acute angle with respect to the lower surface  21 , which edge  24  is aligned along direction A to the corner spacer  50 . 
     The lateral edge  24  defines a rising inclined ramp which connects the lower surface  21  to the upper surface  22  of the base  20  and is extended, substantially continuously, up to the lower edge of the corner spacer  50 . 
     Further, the corner spacer  50  also exhibits a lateral edge  54 , in particular the edge  54  located externally with respect to the separating element  30 , which is inclined by an acute angle with respect to the base  20 . 
     The lateral edge  54  also defines a rising inclined ramp which connects the lower edge of the corner spacer  50  to the upper edge thereof and defines a cam profile on which, by means of a thrust along direction A exerted on the lateral edge  54 , a tile P translating with respect to the device  10  along the direction A can easily cause a lowering of the corner spacer from the raised position to the lowered position, where necessary. 
     In particular, both the corner spacers  50  exhibit respective inclined lateral edges  54 , just as the base  20  exhibits two of the lateral edges  24  opposite one another and extending with respect to the lateral edges  54  of the respective corner spacer  50 . 
     In this case too the corner spacers  50  each comprise a block  51  slidably associated, telescopically, to the base  20  and is provided with fracture ribs  53  able to temporarily retain the block  51 , and therefore the lateral flanks  52  thereof in the raised position. 
     As in the previously-described embodiment, in this embodiment too the fracture ribs  53  are advantageously defined below the plane defined by the upper surface  22  of the base  20 , such that the part remaining attached to the base does not disturb the planarity of the tile P resting thereon. 
     In practice, the base  20  exhibits two through-slots  23  in which the respective blocks  51  can substantially snugly slide; the fracture ribs  53  are defined at the upper edge of each slot  23  and the lower edge of the blocks  51 ; in this way in the raised position the block  51  is maintained by the fracture ribs  53  at a higher level than the base  20 , while once the fracture ribs are broken the block  51  can slide internally of the slot  23  and descend to below the level of the base itself. 
     The height of the block  51  can also be slightly greater than the thickness of the base  20 , especially should the slot  23  pass from side to side of the base  20 ; the exceeding part of the block  51 , in use, can sink into the mortar on which the device  10  is arranged without however interfering with the tile P. 
     In the light of the above description, the functioning of the device  10  is as follows. In order to clad a surface with a plurality of tiles P, first a layer of adhesive is spread on the ground and the tiles P laid on it. 
     In practice, where the first tile is to be arranged, it is sufficient to position a first device  10 , the base of which  20  is destined, for example, to be located below four corners of four respective tiles P. 
     Once the base  20  has been positioned, as can be seen in  FIG. 2 , it is sufficient to position the four tiles P in such a way that each corner thereof exhibits a portion of the lateral flank in contact respectively with a lateral flank  31  of the separator element  30  and a lateral flank  52  of one of the blocks  51 . 
     In this way the squared arrangement is guaranteed, as is the equal distance between the four tiles surrounding the device  10 . 
     When for example the tiles P exhibit particularly large dimensions, it is possible to position a device  10  also at a median zone of the lateral flank of the tile P, as can be seen in  FIG. 2 . 
     In this configuration, the base  20  is placed below at most two flanked tiles P, such that the lateral flank of each of them rests on the lateral flanks  31  of the separator element  30 . 
     In doing this the tile P rests on the corner spacer  50 , which is brought, for example thanks to the weight of the tile P or forced by the operator doing the laying, from the raised position to the non-interfering position in which it is lowered below the level of the upper surface  22  of the base  20 . 
     It is, for example, possible to work by first laying a tile P and then, at the corner or a flank thereof, a base portion  20  of the device can be inserted below the tile P. 
     For example, in relation to the embodiment shown in  FIGS. 15-18 , but for example also in figures from  3  to  9 , in a case in which the base  20  is inserted below the tile P at a lateral flank thereof, the reciprocal translation between the tile P and the base  20  and the lowering of the corner spacer  50  from the raised position to the lowered position are facilitated by the lateral edge  54 , defining the rising inclined ramp which connects the lower edge of the corner space  50  to the upper edge thereof, and, possibly, also from the underlying lateral edge  24 , defining the rising inclined ramp connecting the lower surface  21  to the upper surface  22  of the base  20 . 
     It is possible that one or more of the blocks  51  can be removed, thanks to predetermined fracture ribs entirely similar to the ones described herein above, by the personnel working on the laying, before actually laying, such that in any case the device  10  is suitable for being arranged at the corners of the tiles P (for example none or a single block  51  is removed, for example lowered) or at the sides thereof (for example when both blocks  51  are removed, for example lowered). 
     Once the various bases  20  with the respective separator elements  30  and corner spacers  50  have been positioned as described above, as long as the adhesive has not yet completely solidified, the various wedge elements  40  are inserted to complete the spacing/levelling device  10 , which by pressing on the in-view surface of the tiles P, locally in the various points (median or corner), enable a perfect levelling of the in-view surfaces of the tiles. 
     The invention as it is conceived is susceptible to numerous modifications and variants, all falling within the ambit of the inventive concept. 
     Further, all the details are replaceable by other technically-equivalent elements. 
     In practice the materials used, as well as the contingent forms and dimensions, can be any according to needs, without the invention&#39;s forsaking the ambit of protection of the following claims.

Summary:
An intake manifold ( 2 ) of comburent air is presented for an internal combustion engine ( 1 ) provided with a recirculating conduit ( 60 ) of exhaust gases. The intake manifold ( 2 ) includes a first inlet mouth ( 213 ) of the comburent air, a second inlet mouth ( 214 ) in communication with the recirculating conduit ( 60 ) of the exhaust gases, and a plurality of outlet mouths ( 201 ), having a wall ( 7 ) positioned in front of each of the outlet mouths ( 201 ) and configured for dividing the internal volume of the intake manifold ( 2 ) into two chambers ( 215, 204 ), the first chamber ( 215 ) being placed in communication with the first inlet mouth ( 213 ) and the second inlet mouth ( 214 ) and the second chamber ( 204 ) being placed in communication with the outlet mouths ( 201 ), the wall ( 7 ) defining an opening ( 70 ) adapted for placing the first chamber ( 215 ) and the second chamber ( 204 ) in communication.