Patent Publication Number: US-2023143792-A1

Title: Sensorised wheel hub unit for vehicles, associated system and method for detecting final loads on wheels

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of, and claims the benefit under 35 U.S.C. § 120 of the earlier filing date of, copending U.S. Ser. No. 17/408,705 filed Aug. 23, 2021, which is based on and claims priority to Italian Patent Application No. 102020000020608 filed on Aug. 28, 2020, under 35 U.S.C. § 119, the disclosures of which are incorporated by reference herein. 
    
    
     FIELD 
     The present disclosure relates to a sensorised wheel hub unit for vehicles. 
     BACKGROUND 
     In the suspension units currently in use, sensors are capable of detecting the rotation speed of each wheel of a vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments in accordance with this disclosure will now be described with reference to the accompanying drawings illustrating a non-limiting embodiment in which: 
         FIG.  1    diagrammatically illustrates, in side elevation and partly radial cross-section, a view of a vehicle suspension assembly equipped with a sensorised wheel hub unit in accordance with this disclosure; 
         FIG.  2    diagrammatically illustrates, on an enlarged scale, a three-quarter front perspective view of the detection system in accordance with this disclosure, including an outer ring of the wheel hub unit in  FIG.  1   ; 
         FIG.  3    diagrammatically illustrates, on a further enlarged scale, a detail of a view of the vehicle suspension assembly in  FIG.  1    in cross-section along the line III-III; 
         FIG.  4    diagrammatically illustrates a three-quarter front perspective view of some of the main components of the detection system in  FIG.  2   ; 
         FIG.  5    diagrammatically illustrates, on an enlarged scale, a perspective view of a detail of the outer ring of a wheel hub unit forming part of the detection system in  FIG.  2   ; 
         FIG.  6    diagrammatically illustrates a plan view from above of the same detail as in  FIG.  5   ; 
         FIGS.  7  and  8    illustrate components of the detection system in  FIG.  2    on a larger scale; 
         FIG.  9    illustrates a block diagram of the detection method in accordance with this disclosure using the detection system in  FIG.  2   ; 
         FIG.  10    diagrammatically illustrates, on an enlarged scale, two views at right angles, in plan (above) and in elevation (below), of a sensor constructed in accordance with this disclosure; 
         FIG.  11    diagrammatically illustrates a radial cross-section of the sensorised wheel hub unit in  FIG.  1   ; 
         FIG.  12    diagrammatically illustrates, on an enlarged scale, a radial longitudinal cross-section of an outer ring of the wheel hub unit in  FIG.  1   ; and 
         FIG.  13    illustrates a plan view radially from outside the outer ring in  FIG.  12   . 
     
    
    
     DETAILED DESCRIPTION 
     While known sensors that are actually in use in vehicles are capable of detecting the rotation speed of each wheel of a vehicle, no use is made of sensorised suspension units capable of detecting the stresses arising from the different driving conditions of the vehicle upon the wheel hub unit on which the vehicle&#39;s wheel is mounted, e.g., those due to the roughness or different conditions of the surface over which the vehicle is moving, and/or the manoeuvres performed, e.g. steering, braking, etc. 
     U.S. Pat. No. 6,619,102B2 describes a wheel hub unit consisting of a rolling bearing, an outer ring having a flange for attachment to the suspension strut, provided with circumferential and radial elastic deformation zones to each of which a single deformation sensor is applied. This solution is complex and costly to implement and has not proved effective for correctly detecting the forces acting on the wheel hub unit. 
     U.S. Pat. No. 6,658,943B2 describes a double-row tapered roller bearing in which the radially outer cylindrical lateral surface of the bearing outer ring is provided with four angularly spaced sensor modules fixed circumferentially on the cylindrical surface. Each module consists of a pair of strain sensors positioned at 90° to each other. Again, this solution has also not proved to be effective in correctly detecting the forces acting upon it. 
     These solutions use, as sensor modules, strain gauges generally adhesively bonded to the surfaces to be detected, a solution which has proved to be ineffective and above all unreliable, and which requires successive recalibrations of the sensor. In effect, all known systems are only suitable for testing, and are not suitable for, or compatible with, series production. 
     This disclosure is directed to improved sensorised wheel hub units for vehicles. This disclosure further relates to a detection system and an associated method for accurately detecting the forces and moments applied to the wheel hub unit in real time so as to provide the vehicle control unit with useful information to improve control of stability and make it more effective, as well as usable for the better management of autonomous driving functions. 
     With reference to  FIGS.  1  to  4   , the reference numeral  1  relates to a vehicle suspension assembly as a whole, which includes a sensorised wheel hub unit  2  and a suspension strut or articulation  3  for a wheel hub unit  2 . A wheel hub unit  2 , which is configured to couple with a suspension strut or articulation  3 , includes a detection system  4  ( FIG.  2   ) configured to detect mechanical stresses such as loads, in particular forces and moments (torques), acting on a wheel hub unit  2 . 
     Some embodiments of a wheel hub unit  2  include a rolling bearing  34  in turn comprising a radially outer ring  5  and a radially inner ring  35 , an annular flanged hub  6  radially coaxially inserted on the inside of the radially outer ring  5  and immobilisably angularly coupled to the inner ring  35  and a plurality of rolling elements  9  ( FIG.  1   ) inserted between the outer ring  5  and the flanged hub  6 , in this case between the outer ring  5  and the inner ring  35 , in order to cause the flanged hub  6  to be able to rotate with respect to the outer ring  5 , which is stationary when in use since it is linked/attached to the suspension strut or articulation  3 . In this way, a flanged hub  6  is inserted so it idles coaxially inside the outer ring  5 . 
     In particular, the flanged hub  6  is inserted into the radially outer ring  5  of the rolling bearing  34  from the side of a first extremity  7  ( FIGS.  1  and  2   ) of the outer ring  5  which in use faces towards the outside of the vehicle and, in the example illustrated, towards a flange  8  of the hub  6  radially extending beyond the outside of the hub  6 . In the illustrated non-limiting example, the rolling elements  9  consist of two ball bearings  9 . In other embodiments the rolling elements may be cylindrical or tapered or any suitable rolling element as one will appreciate upon reading this disclosure in its entirety. 
     In any event, the rolling elements  9  are configured to engage two respective annular races  10  formed radially on the inside of the outer ring  5 , on its radially inner lateral surface  11 , which in the illustrated example is substantially cylindrical, as illustrated diagrammatically in  FIGS.  1  and  2   . 
     In a known way, the rolling elements  9  also engage corresponding annular races, which are known and for simplicity not described, formed radially on the outside of the inner ring  35  or, if this is not present, directly on the hub  6 . 
     According to some embodiments, the detection system  4  comprises a plurality of longitudinal concave recesses  12  ( FIGS.  2 ,  5  and  6   ) formed axially in a radially outer cylindrical lateral surface  13  of the outer ring  5 , spaced angularly apart from each other. 
     Each recess  12 , which thus forms an integral part of the outer ring  5 , extends over an annular race  10  for the rolling elements  9 , in the non-limiting but preferred embodiment illustrated over both races  10 , in a circumferential direction relative to them, thus circumferentially over each race  10 . 
     Here and hereafter, the term “circumferentially” with respect to the recesses  12  is to be understood as extending so as to “cover” a respective circumferential section of each race  10 , irrespective of whether a recess  12  is shaped so as to have a curvature parallel to that of the surface  13  or forms a flat portion oriented parallel to a geometric chord of the surface  13 . The recesses  12  are configured to define corresponding zones of localised elastic deformation in the outer ring  5 . 
     In the embodiment illustrated, four recesses  12  are provided on the outer lateral surface  13 , spaced at regular angular intervals, thus arranged at 90° from each other. The recesses  12  could however be present in a different, greater or lesser, number (at least two) and be arranged with non-identical angular intervals between them, some circumferentially closer to others, depending on specific requirements relating to the geometry of the suspension assembly  1 . 
     According some embodiments and also with reference to  FIG.  13   , a detection system  4  further comprises a first annular step  14 , formed peripherally within each recess  12  along the whole perimeter P of the recess  12  and in a position immediately adjacent to the perimeter P. 
     For each recess  12 , such a detection system  4  further comprises at least one metal plate  15  located transversely within each recess  12 , thus oriented in a circumferential direction with respect to the outer ring  5 , so as to be substantially aligned circumferentially with an annular race  10 . In the example illustrated, there are therefore two metal plates  15 , housed transversely within each recess  12 , parallel to each other and close to opposite axial ends  16  of corresponding recess  12  ( FIGS.  5 ,  12  and  13   ), each metal plate  15  being substantially aligned circumferentially over a corresponding race  10 , in particular over a circumference which can be traced on race  10  where the points of contact between the balls  9  and the race  10  lie. 
     According some embodiments, circumferentially opposite extremities  17  of each metal plate  15  (in the meaning defined above, that is aligned with each other in a circumferential direction with respect to the ring  5 ) are welded to opposite lateral sides  18  of the first step  14 . This method of attachment by welding, in contrast to other possible methods, such as adhesive bonding, has proved to be surprisingly more effective in ensuring the reliability of the results provided by the detection system  4 , as will be seen, as well as improving the process of manufacturing the outer ring  5  with at least part of the detection system  4  incorporated with it. 
     In plan, the metal plates  15  may preferably be in the shape of an “H” oriented in an axial direction ( FIGS.  5 ,  6  and  10   ), having a middle portion  19  of narrow width with respect to the outer ring  5  in an axial direction connecting the two extremities  17 , thus forming the crossbar of the H, while the stems of the H are formed by the opposite extremities  17  of the plate  15 . 
     With reference to  FIGS.  10  and  11   , the extremities  17  have a width Ws in an axial direction with respect to the outer ring  5  that is larger than the width Wr of the middle portion  19 , again measuring this width in an axial direction with respect to the outer ring  5 . In certain embodiments, following relationship is preferred: 
     
       
         
           
             
               
                 
                   
                     0 
                     . 
                     4 
                   
                   ≤ 
                   
                     
                       W 
                       r 
                     
                     
                       W 
                       S 
                     
                   
                   ≤ 
                   
                     0 
                     . 
                     6 
                   
                 
               
               
                 
                   [ 
                   01 
                   ] 
                 
               
             
           
         
       
     
     Furthermore, with particular reference to  FIG.  11   , according to certain embodiments, following relationship is preferred: 
     
       
         
           
             
               
                 
                   
                     
                       0 
                       . 
                       2 
                     
                     ⁢ 
                     5 
                   
                   ≤ 
                   
                     
                       L 
                       S 
                     
                     
                       P 
                       
                         B 
                         ⁢ 
                         p 
                       
                     
                   
                   ≤ 
                   
                     
                       0 
                       . 
                       7 
                     
                     ⁢ 
                     5 
                   
                 
               
               
                 
                   [ 
                   02 
                   ] 
                 
               
             
           
         
       
     
     where: Ls is the length of the plates  15  between their opposite extremities  17  and P Bp  is the geometric projection onto the recesses  12  of the circumferential pitch Pa of the balls  9  within the solid angle defined by the angular pitch γ Bp  of the balls  9  themselves. 
     In addition, the thickness Ts (in mm) of the plates  15  must comply with the following relationships: 
     
       
         
           
             
               
                 
                   
                     0 
                     . 
                     3 
                   
                   ≤ 
                   
                     T 
                     ⁢ 
                     s 
                   
                   ≤ 
                   
                     0.6 
                         
                     and 
                     ⁢ 
                     
                         
                          
                     
                     ⁢ 
                     
                       
                         T 
                         S 
                       
                       
                         L 
                         S 
                       
                     
                   
                   ≤ 
                   
                     0 
                     . 
                     1 
                   
                 
               
               
                 
                   [ 
                   03 
                   ] 
                 
               
             
           
         
       
     
     According to one aspect of embodiments in accordance with this disclosure, the detection system  4  also includes a hollow  20  formed centrally within each recess  12  and bounded perimeterally by the first annular step  14  so as to form a second step  21  inside the first step  14  within the recess  12 , delimiting a base wall  22  of the recess  12 . 
     In embodiments in accordance with this disclosure, the base wall  22  of the hollow  20  is flat and parallel to a geometric chord of the curved cylindrical surface  13 , and the steps  14  and  21  are also bounded by flat surfaces parallel to said geometric chord. However, the recesses  12  may also be made curved, rather than flat, so that the base wall  22  may be curved and parallel to the curvature of the lateral surface  13  in which the recesses  12  are formed, just as the surfaces bounding the steps  14  and  21  may also be curved and parallel to the surface  13 . 
     In embodiments in accordance with this disclosure, each metal plate  15  spans the hollow  20 , but is spaced apart from it and the base wall  22  thereof. 
     In particular, in the non-limiting example illustrated, the narrow central portion  19  of each metal plate  15  spans the hollow  20  and is spaced apart from it. 
     In this way, there is always a predetermined gap between each plate  15  and the base wall  22  of each recess  12 , as a result of which, no metal plate  12  ever touches the base wall  22  of the respective recess  12 , even when there is localised elastic deformation in the race section  10  below the recess  12 , due for example to the passage of the rolling elements  9  under particularly severe local loading conditions. 
     The detection system  4  comprises a load sensor S for each metal plate  15 , and, this sensor consists of a plate  23  of piezoresistive ceramic material ( FIGS.  5  and  6   ) made to be of one piece with the metal plate  15 , preferably spanning the narrow middle portion  19  of the metal plate  15 , when present, and in any event positioned to span the hollow  20 . 
     The use of piezoresistive ceramic plates structurally incorporated with the metal plates  15 , instead of strain gauges as in the known art, has proved to be successful in achieving high reliability for the detection system  4  and easy industrialisation of it and the corresponding outer ring  5  with which it is incorporated. 
     Preferably, the ceramic plates  23  are obtained by the direct deposition of piezoresistive ceramic material onto the corresponding plates  15 , for example on the narrow middle portion  19 , and as far as near to the opposite extremities  17  of each metal plate  15 , for example by means of screen printing or any other suitable method. 
     In plan, the recesses  12  have a rectangular shape with rounded edges defined by a flared edge  24 , rounded so as to adopt a curved concave shape bounding the perimeter P, from which the first annular step  14  and then the hollow  20  defining the second step  21  forming the base wall  22  depart in succession from the edge  24  towards the centre of the recess  12 . 
     The recesses  12  therefore have a depth in the radial direction (with respect to an axis of symmetry A of the outer ring  5 — FIG.  2   ) defined by the sum of the height from the edge  24  to the step  14  and the height of the next step  21  formed by the hollow  20 , up to the base wall  22 . 
     The recesses  12  may be of identical depth, or some recesses  12  may be to a greater or lesser extent deeper than others, bearing in mind that when in use the greater the depth of a recess  12 , the greater will be the electrical signal associated with the load sensors defined by the ceramic plates  23  and the respective metal plates  15  housed within that recess  12 , and, on the other hand, the greater will be the structural weakening caused to the outer ring  5  by the presence of the recesses  12 . 
     Thus, using recesses  12  of different depths can mediate between these two opposing requirements. 
     In embodiments in accordance with this disclosure, the depth of the recesses  12  ( FIG.  12   ) must nevertheless comply with the following relationship: 
     
       
         
           
             
               
                 
                   
                     0 
                     ⁢ 
                     
                       .05 
                       · 
                         
                       
                         ( 
                         
                           
                             
                               ( 
                               
                                 
                                   D 
                                   OR 
                                 
                                 - 
                                 
                                   P 
                                   
                                     D 
                                     ⁢ 
                                     i 
                                     ⁢ 
                                     a 
                                   
                                 
                               
                               ) 
                             
                             
                               2 
                               ⁢ 
                                  
                               
                                 cos 
                                 ⁡ 
                                 ( 
                                 
                                   α 
                                   B 
                                 
                                 ) 
                               
                             
                           
                           - 
                           
                             R 
                             Ball 
                           
                         
                         ) 
                       
                       · 
                       cos 
                     
                     ⁢ 
                     
                       ( 
                       
                         α 
                         B 
                       
                       ) 
                     
                   
                   ≤ 
                   
                     P 
                     
                       D 
                       ⁢ 
                       1 
                       ⁢ 
                       s 
                       ⁢ 
                       t 
                     
                   
                   ≤ 
                   
                     
                       0.4 
                       · 
                       
                         ( 
                         
                           
                             
                               ( 
                               
                                 
                                   D 
                                   OR 
                                 
                                 - 
                                 
                                   P 
                                   
                                     D 
                                     ⁢ 
                                     i 
                                     ⁢ 
                                     a 
                                   
                                 
                               
                               ) 
                             
                             
                               2 
                               ⁢ 
                                  
                               
                                 cos 
                                 ⁡ 
                                 ( 
                                 
                                   α 
                                   B 
                                 
                                 ) 
                               
                             
                           
                           - 
                           
                             R 
                             Ball 
                           
                         
                         ) 
                       
                       · 
                       cos 
                     
                     ⁢ 
                     
                       ( 
                       
                         α 
                         B 
                       
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   04 
                   ] 
                 
               
             
           
         
       
     
     where: D OR  is the outer diameter of the outer ring  5 , P Dia  is the “Ball Pitch Diameter”, that is the diameter of the circumference on which the geometric centres of the balls  9  lie, R Ball  is the radius of the balls  9 , α B  is the angle formed between the point of contact between the balls  9  and the radial perpendicular to the axis A and P D1st  is specifically the depth of a recess  12 , which must therefore be between 0.05 and 0.4 times the difference between the diameter of the external surface  13  of the outer ring  5  D OR  and the point of ball-race contact in a radial direction given by the difference [(D OR −P Dia /2 cos(α B )−R Ball ] along the direction defined by the contact angle (α B ). 
     As already seen, in some embodiments, the wheel hub unit  2  is provided with a radially outer ring  5  having a pair of races  10  for rolling elements  9 , arranged axially in tandem, and each ceramic load sensor S has a plate  23  of piezoresistive material fixed onto a respective metal plate  15 , for example spanning the narrow intermediate portion  19 , when present. 
     In addition, each recess  12  accommodates within it a pair of metal plates  15  arranged parallel to each other and positioned substantially circumferentially and axially in relation to the pair of races  10  with the plates  23  spanning the hollows  20 . 
     Thus, in this preferred embodiment, the outer ring  5  is provided with four recesses  12 , identically or differently spaced apart from each other by the same or different angles. 
     In embodiments in accordance with this disclosure, the axial distance or “pitch” or spacing Is between two sensors S housed in the same recess  12  must comply with the following relationship ( FIGS.  12  and  13   ): 
       0.8·( A   Bp −( D   OR −2· P   D1st   −P   Dia )· tg (α B ))≤ I   S  
 
       where:≤1.4·( A   BP −( D   OR −2· P   D1st   −P   Dia )· tg (α B ))
 
     A Bp  is the axial distance between the geometric centres of the balls  9  engaging the two different races  10  of said pair of races  10 , between the two ball bearings, D OR  is as defined above, P D1st  is as defined above, that is calculated using relationship [04], and P Dia  and α B  are as defined above. 
     Relationship [05] above therefore implies that the spacing between centre lines I s  between the two sensors S in the axial direction must always be between 0.8 and 1.4 times the difference between the axial distance between the primitive diameters of the two rings of rolling elements, that is the balls  9  (A Bp ) and the projection in the axial direction of the difference between the point of intersection between the directrix defined by the contact angle (α B ) and the surface  13  of the outer ring  5  less the depth of the recess  12  under consideration and the primitive diameter of a ring of rolling elements (P Dia ). 
     According to a possible variant, which is not illustrated for the sake of simplicity, each recess  12 , instead of being rectangular in shape, has an S-shape in plan with a rounded perimeter profile always bounded by a rounded perimeter edge  24  immediately adjacent to the first step  14 , so that the pair of metal plates  15  and respective plates  23  housed in each recess  12  are arranged angularly offset from each other. This solution may be advantageous in certain specific mechanical stress situations, depending on the geometry of the suspension assembly  1 . 
     Finally, the detection system  4  comprises an electrical circuit  25  ( FIGS.  2  and  4   ) connected to the opposite extremities of each ceramic plate  23  facing the circumferential extremities  17  of the respective metal plate  15  to collect a first electrical signal S 1  relative to each sensor, and then to collect a plurality of signals S 1 , illustrated by arrows in  FIG.  9   . 
     A ceramic plate  23  constituting each load sensor is borne by a first face  26  of the respective metal plate  15  opposite the radially external lateral surface  13  of the outer ring  5  and, as already indicated, the ceramic plate  23  is formed in such a way as to be entirely and always in contact with said first face  26 , completely attached to the same, being of one piece with the same, for example printed directly onto the first face  26  of the respective metal plate  15 . 
     According to embodiments in accordance with this disclosure, a detection system  4  further comprises a temperature sensor  27  ( FIG.  3   ) supported by the electrical circuit  25 , integral with it and housed in a blind hole  29  formed on the outer lateral surface  13  of the outer ring  5 . 
     As is well illustrated in  FIG.  2   , the electrical circuit  25  is connected in symmetrically opposite positions in the circumferential direction to opposite extremities of each ceramic plate  23  to collect a plurality of first electrical signals S 1  ( FIG.  9   ), each relating to a respective sensor  23 ; the electrical circuit  25  is also connected to the temperature sensor  27  (with which it is integrally connected) to collect a second electrical signal S 2  emitted by the same ( FIG.  9   ). 
     A circuit board  30 , illustrated diagrammatically by dashed lines as a block in  FIGS.  2  and  4   , is connected to one end  31  of the electrical circuit  25  to simultaneously process the first signals S 1  relating to each sensor  23  and the second signal S 2  relating to the temperature sensor  27  in parallel, as will be seen. 
     In various embodiments in accordance with this disclosure, illustrated in  FIGS.  2  and  4   , the electrical circuit  25  consists of a flat T-shaped multipolar conductor  32  comprising two opposite first arms or branches  33  aligned with each other, a middle portion  36  connecting the first arms  33  to each other, which project from the middle portion  36  on opposite sides, and a third arm or branch  37  projecting from the middle portion  36  perpendicularly to the first arms  33 . 
     The first arms  33  bear laterally respective projecting opposite pairs of Y-shaped contacts  38 , and each pair of contacts  38  is electrically and mechanically connected to the opposite extremities of a respective ceramic plate  23 , preferably by brazing. 
     The middle portion  36  includes ( FIG.  3   ) a metal plate  39 , illustrated in detail in  FIG.  8   . The temperature sensor  27  is soldered (brazed) to the flexible circuit formed by the multipolar flat conductor  32  at the metal plate  39 , essentially on the middle portion  36  at a position adjacent to the metal plate  39 . 
     On the other hand, the metal plate  39  has the function of centring and mechanically retaining the flexible conductor  32  and a protective rubber overmoulding  42  as illustrated below. 
     The middle portion  36  is supported on the plate  39  and a section of the arm or branch  37  of the flat conductor  32  is also supported and incorporated immediately adjacent to the middle portion  36 . 
     The metal plate  39  is configured so as to be anchored in the blind hole  29  of the outer ring  5  to house the temperature sensor  27  therein. For this purpose, it includes a hook-shaped end  40  configured to fit into the blind hole  29 . 
     The third arm  37  is provided over the middle portion  36  with an integral protective sheath  41  ( FIG.  7   ) of a sealing transverse element  42  overmoulded onto the metal plate  39  and incorporating part of the metal plate  39 , configured when in use to fit between the outer lateral surface  13  of the outer ring  5  and the suspension strut or articulation  3  coupled to the wheel hub unit  2 . 
     The protective sheath  41  has the function of protecting the flexible circuit  25  from impacts with stones and aggressive atmospheric agents in the exposed section, as well as having the function of a special seal at the interface between the wheel hub unit  2  and the suspension strut or articulation  3  on one side and with a box  44  on the other side; the latter box houses an offtake to connect the electrical circuit  25  to a cable  45  that can be connected to a vehicle control unit (ECU) or directly houses a data-processing circuit board ( 30 ). 
     The box  44 , preferably made by moulding from a synthetic plastics material in the form of two half-shells joined together, for example by screws, is provided in the example illustrated by a side cable  45  configured to connect in a known way, not illustrated for simplicity, with a vehicle control unit or other interface device. 
     In order to adequately support the sheath  41  together with the sealing element  42 , imparting adequate rigidity to it, it is co-moulded onto the plate  39 , which is provided with appropriate L-shaped and/or U-shaped brackets  46  from the opposite side to its hook end  40 . 
     In certain embodiments in accordance with this disclosure, the first arms  33  are configured to wrap in a ring around the outer lateral surface  13  of the outer ring  5 , within an annular groove  28  therein. 
     On the side of the outer lateral surface  13  of the outer ring  5 , the arms  33  are preferably provided with wings or double-sided adhesive elements  47  having exactly the same transverse dimension as the annular groove  28  in order to be able to exactly centre the arms  33  of the multipolar conductor  32  forming the electrical circuit  25  within the annular groove  28  and, consequently, to precisely position the contacts  38  radially outside and above the ceramic plates  23 . 
     After the outer ring  5  has been manufactured in the conventional way and the recesses  12  have been formed on its external lateral surface  13  with the two concentric steps  14  and  21 , generally by chip removal, the metal plates  15 , which have already been integrally provided with the piezoresistive ceramic plates  23  that are fully bonded in contact with and completely of one piece with the plates  15  over their entire length or at least all of the centre portion  19 , are housed therein, resting their extremities  17  on the step  14 . 
     Then a welding operation or step, preferably performed by laser, is performed between the whole transverse edge of each extremity  17  and the step  14 , thus mechanically binding the metal plates  15  to the outer ring  5  in each recess  12  without causing the plates  15  to touch the base wall  22  of the respective recess  12 . 
     Then (or in parallel), the electrical circuit  25  is made with the corresponding T-shaped multipolar flat conductor  32 , pre-formed as a set of conducting and insulating and protective layers housing the electrical connecting lines between the sensors, the temperature sensor and the two connectors at the tip of the branch  41  of the flexible conductor or “flex” which connect the flex to the control unit or via a cable (which then goes to the control unit); in this step, the contacts  38  can be made of one piece with the conductor  32 , by moulding, or be attached to it later. In this step, the components assembled on the flex are eight sensors, a temperature sensor and two “board to board” connectors, which are all soldered to the flex by a soldering operation in a controlled oven using a “pick and place” machine and a thermal “reflow” treatment (typical of electronic applications), so that eventually every Y-contact, which electrically configures a pair of opposite contacts electrically insulated from each other, is connected to the respective internal conductor wires/lines (not illustrated for simplicity) of the multipolar conductor  32 . 
     A final process of rubber overmoulding of the sheath  41  provides protection and insulation for the flexible circuit  25  (as described above). At this point the flex/sensors/protection sub-assembly is ready for assembly onto the outer ring  5 , by inserting the branches or arms  33  within the annular groove  28  so that the extremity  40  of the plate  39  is positioned within the blind hole  29 . It is then possible to proceed with the operation of laser welding the piezoresistive metal sensors to the already-connected flexible circuit  25  by welding the opposite extremities  17  to the edges of the recesses  12  and thus also attaching the entire circuit  25  to the ring  5 . 
     This is a very delicate operation, and in order to carry it out on an industrial scale it is necessary to select specific dimensional design parameters for the sensors (formed by the plates  23  incorporated onto the plates  15 ), as described below, in order not to damage them during the laser welding operation. 
     The flexible circuit  25  has the function of electrically connecting the sensors to a connector or the cable  45  and then to the vehicle ECU for data processing. 
     A box  44  may be connected to the conductor  32  and its sheath  41  either before or after this step. 
     At this point, a detection system  4  in accordance with this disclosure is ready and is fully integrated with the outer ring  5 , of one piece with its outer lateral surface  13 , and a calibration step can be performed immediately after the wheel hub unit  2  has been completely assembled by mounting the rolling elements  9  in the ring  5  of the flanged hub  6 , so that after this calibration step the sensorised wheel hub unit  2  in accordance with this disclosure constitutes a fully plug-in sensorised unit which no longer requires any calibration by the vehicle assembler. 
     From what has been described so far, some embodiments in accordance with this disclosure also relate to a method for the detection of stresses on wheels comprising the steps of placing a fixed number of load sensors  23  on the outer lateral surface  13  of an outer ring  5  of a wheel hub unit  2 , collecting first electrical signals S 1  associated with the load sensors  23  in real time and processing the first electrical signals S 1  by, for example, the circuit board  30 . 
     However, the load sensors consist of the plates  23  of piezoresistive ceramic material of one piece with the respective metal plates  15 , in a longitudinal direction with respect to the same and circumferential with respect to the outer ring  5 . Furthermore, only the opposite extremities  17  of the metal plates  15  are welded to the outer ring  5  and the welding is oriented in an axial direction with respect to the ring  5  itself. 
     A method in accordance with this disclosure therefore comprises the step of positioning the ceramic plates  23  on the metal plates  15  and housing the metal plates  15  within respective concave recesses  12 , welding them to the same at opposite extremities, the recesses  12  having previously been formed in the outer lateral surface  13  of the outer ring  5  in relation to the respective races  10  for the rolling elements  9 . 
     These steps are performed so that there results a predetermined gap between each metal plate  15 . In particular, a predetermined gap is formed between the narrow middle portion  19  thereof, and a base wall  22  of each recess  12 . 
     The following steps are then carried out using the electrical circuit  25  and a suitably programmed circuit board  30 . 
     Firstly, and with reference to  FIG.  9   , a first step  50  (indicated as a block in  FIG.  9   ) is performed within the circuit board  30  in which all the first electrical signals S 1  relating to the same race  10  are analysed in a comparative way and in real time. 
     This analysis is performed for both amplitude and frequency, since the electrical signals S 1  are pseudo-sinusoidal; in fact the signals S 1  show strong variations in both frequency and amplitude when in use due to variations in vehicle speed and the different manoeuvres performed by the vehicle respectively. 
     When the rolling elements  9  pass over the recesses  12  during the rotation of the flanged hub  6  (which is connected to a vehicle wheel), they place the ceramic plates  23  under tension; the plates  23 , which in theory should not also flex thanks to the gap mentioned, in reality flex anyway because of the unavoidable asymmetry of the welding zones with respect to the neutral line of each plate  15 . However, because it is impossible for them to touch the outer ring  5  as a result of this bending, specifically because of the predetermined gap between plate  15  and based wall  22  discussed above, uncontrollable touch/no-touch situations with consequent unwanted voltage peaks that would make the use of the system impossible are prevented. 
     Since the ceramic plates  23  are made of a piezoresistive material, they change their electrical resistance in proportion to the voltage applied to them, a voltage which, due to the positioning of the plates  23  described, is circumferentially oriented, that is exactly in the direction in which the races  10  extend. 
     The electrical signals S 1  therefore have a pseudo-sinusoidal pattern (that is a substantially sinusoidal pattern but irregular in amplitude) of frequency proportional to the number of rolling elements  9  and the rotation speed of the flanged hub  6 , and of intensity, that is signal amplitude, depending on/proportional to the strength and direction of the applied voltage. In particular, the signal S 1  will be positive for voltages applied to the respective plate  23  that are greater than the preloading to which the wheel hub unit  2  is subjected when in use, and will be negative when the voltage applied to the plates  23  is in a direction and of a strength such as to relax these from the preloading. 
     The signal S 1  therefore changes from negative to positive values as increasing mechanical stress is applied to the plates  23 . 
     The metal plates  15  also provide a secure and effective anchorage for the plates  23  onto the outer lateral surface  13 . 
     The narrow middle portion  19  amplifies the electrical signals S 1  associated with each load sensor  23 . 
     In the first step  50 , a frequency value F1 for one of the races  10  and F2 for the other race  10 , equal to the frequency of the first signals S 1  having the maximum amplitude, are therefore determined, and as many amplitude values A1-An as there are sensors  23  associated with each race  10  are determined. Having determined a common frequency for the signals S 1  relative to the sensors comprising the plates  23  (and the relative plates  15 ) leading to the same race  10 , the maximum amplitude of each signal S 1  generated by each sensor is calculated. 
     In the case of the example illustrated, as there are four recesses  12  each housing two sensors consisting of a piezoresistive plate  23  anchored onto a metal plate  15 , one frequency value F1 or F2 and four amplitude values A1-A4 will be obtained for each of the two races  10  at the output from step  50 , that is to say a total of ten values. 
     Simultaneously and preferably, a second step is performed in which the circumferential temperature of the outer ring  5  is detected by means of the temperature sensor  27  close to or alongside the cylindrical outer lateral surface  13  between the two races  10 . 
     Subsequently, a third step  51  (indicated by a block in  FIG.  9   ) is preferably performed in which the previously determined amplitude values A1-A4 associated with each sensor  23  of each race  10  are corrected according to an extrapolation function previously empirically determined by applying the same mechanical stress to the outer ring  5  at a plurality of different temperatures and determining the maximum amplitude values associated with each sensor  23  for each temperature. 
     In fact, although the variation in electrical resistance in a piezoresistive material is also a function of temperature, the most appreciable variation in the signals S 1 , for the same mechanical voltage applied, depends on the variation in the preloading on the elements of the wheel hub unit  2  caused by a change in temperature which produces differential thermal expansion, due in this case to the way the bearing is mounted on the suspension strut  3 . 
     The extrapolation function used in the third step  51 , which may consist of an algorithm or an interpolation map, is determined in the calibration step mentioned above, which is to be performed after each sensorised wheel hub unit  2  is completed. 
     Corrected amplitude values D1-Dn are obtained for each race  10  from the third step  51 , in the example illustrated four plus four values, that is eight amplitude values D1-D8 in all, associated with two frequency values F1, F2 as previously processed, for a total of 10 signal values. 
     In a fourth and final step  52  (indicated by a block in  FIG.  9   ), the temperature-corrected amplitude values D1-D8 and the previously determined frequency values F1, F2 for both races  10  are processed to calculate the forces and moments applied to the outer ring  5  in real time, extrapolating them by means of a calibration function or map. 
     This calibration map will have been previously determined empirically by applying a plurality of first combinations of known forces and moments to the outer ring  5  and associating a second combination of maximum amplitude and frequency values determined by means of the previous steps with each first combination. This calibration map  58  is also obtained during the calibration step to which each wheel hub unit  2  is subjected as soon as it is completed. 
     Substantially, in the calibration step, after the relationship between temperature variation and the value which is to be assumed to be the correct value of the signal amplitude for each sensor  23  has been determined, different sets of forces and torques of known modulus and direction are applied to the outer ring  5  and the map points relating the amplitudes and frequencies to the applied loads will be determined using non-linear regression for different rotation speeds of the flanged hub  6 ; e.g., for a force of 20 kN, a frequency of 20 Hz and amplitude values of 10, 8, 3 and 1 will be determined on a race  10 . It can therefore be assumed that when in use the circuit board  30  processes these frequency and amplitude values, a force of 20 kN will have been applied to the outer ring  5 . 
     Through continuing to apply several known sets of forces and/or torques, a plurality of map points  59  having particular associated frequency and signal amplitude values will thus be obtained. Through interpolating between these map points, in use it will therefore be possible to determine all the forces and torques applied to the outer ring  5  at any time in real time. On will appreciate that map  58  may be stored within memory of, e.g., circuit board  30 , or, e.g., within memory that is communicably coupled to circuit  30  so that it may be accessed or referenced, e.g., the process illustrated in  FIG.  9   . 
     On the basis of the above, it is clear that in some embodiments, the second and third steps can be omitted and it is possible to go from the first to the fourth step directly, dispensing with the calculation of correct amplitude values and using the values selected in the first step A1-An in the fourth step. 
     Conversely, in other embodiments, the second and third steps described above will also be performed. 
     In this case, the amplitude values (A1-An) associated with each sensor and previously determined in step a) will be corrected using two correction functions: an empirically calculated thermal correction depending on the temperature detected in the second step and a correction to the frequency previously calculated for each race in order to determine corrected amplitude values D1-Dn; subsequently, the fourth step will be performed, but with processing the corrected amplitude values D1-Dn to calculate the forces and moments applied to the outer ring  5  in real time, extrapolating them using a map previously determined empirically through a non-linear regression function. 
     In this way, during the normal operation of the wheel hub unit  2 , the longitudinal, lateral and vertical forces applied to the outer ring  5  when running, as well as the self-aligning torque or moment, can be determined with a suitable number of available recesses  12 . 
     This information, that is the values of the forces and moments acting on the outer ring  5  calculated in step  52 , will then be provided to the vehicle control unit via the cable  45  in real time, and the unit will be able to use them to improve functions of the vehicle control unit. For example, such functions include as ABS, ESP, ECU, vehicle dynamics, engine control, suspension control, and the like. 
     The object of the present disclosure is to provide a sensorised wheel hub unit and an associated system and method for real-time, accurate and reliable detection of the magnitude of applied forces and moments, that is the loads to which a vehicle is subjected when driven, and which are at the same time easy for the vehicle manufacturer to implement. 
     According to the disclosure, a sensorised wheel hub unit and an associated detection system and method having the characteristics set out in the appended claims are therefore provided. All the aims of this disclosure are therefore achieved. 
     For example, in some embodiments, a sensorised wheel hub unit including a system for detecting mechanical stress and including a rolling bearing bounded radially by an outer surface and provided radially on the inside with at least one annular race for rolling elements; in which the detection system comprises a plurality of zones of elastic deformation defined by respective angularly spaced longitudinal recesses axially formed on the outer surface of the outer ring, each recess extending over a circumferential length of the annular race; wherein the detection system in additionally includes: a first annular step formed peripherally within each recess along the whole perimeter (P) of the same and in a position immediately adjacent to the perimeter (P); at least one metal plate located transversely within each recess, aligned in a circumferential direction to the annular race, circumferentially opposite extremities of the metal plate being welded to opposite lateral sides of the first step; a hollow formed centrally within each recess and bounded perimeterally by the first annular step so as to form a second step inside the first step, delimiting a base wall of the recess, the metal plate spanning the hollow so as to be spaced apart from, and never touch, the base wall of the recess; a sensor consisting of a plate of piezoresistive ceramic material made to be of one piece with the metal plate, spanning the hollow; and an electrical circuit connected to opposite extremities of the ceramic plate facing the circumferential extremities of the metal plate to collect an electrical signal (S 1 ) relative to each sensor. 
     In further example, in some embodiments, a system for real-time detection of the forces and moments applied to a wheel hub unit including an outer ring radially provided on the inside with a pair of annular races for rolling elements includes: a plurality of longitudinal recesses axially formed in an outer lateral surface of the outer ring, spaced angularly apart from each other, each recess extending both axially and in a circumferential direction over both the annular races, the recesses being configured to define zones of localised elastic deformation in the outer ring; a first step, of annular shape in plan, formed peripherally within each recess along the whole perimeter of the same; a pair of metal plates located transversely within each recess, each aligned circumferentially with a respective annular race, circumferentially opposite extremities of the metal plates being welded to opposite lateral sides of the first step; a hollow formed centrally within each recess and bounded perimeterally by the first annular step ( 14 ) so as to form a second step inside the first step, delimiting a base wall of the recess, the metal plates spanning the respective hollow so as to be spaced apart from, and never touch, the base wall of the recess; a plurality of respective sensors consisting of plates of piezoresistive ceramic material made to be of one piece with the metal plates on a first face thereof opposite to the radially outer lateral surface of the outer ring; a temperature sensor; an electrical circuit connected in symmetrically opposite positions in the circumferential direction to opposite extremities of each ceramic plate to collect a plurality of first electrical signals (S 1 ), each relating to a respective sensor, the electrical circuit being also connected to the temperature sensor to collect a second electrical signal (S 2 ) emitted by the same; and a circuit board connected to one end of the electrical circuit to simultaneously process the first signals (S 1 ) relating to each sensor and the second signal (S 2 ) relating to the temperature sensor in parallel. 
     In further example, a method for the detection of stresses on wheels includes the steps of placing a fixed number of load sensors on an outer lateral surface of an outer ring of a wheel hub unit, collecting first electrical signals associated with the load sensors in real time and processing the first electrical signals; such that the step of fitting load sensors requires the prior formation of a plurality of concave recesses on the outer lateral surface of the outer ring over respective rolling races for rolling elements, the forming of plates of piezoresistive ceramic material of one piece with the respective metal plates and housing the metal plates within respective recesses, welded within the same and in such a way that there is a predetermined gap between the metal plates and a base wall of each recess; and in that the method also includes: a) analysing the amplitude and frequency of the first electrical signals (S 1 ) relating to the same race in a comparative way and in real time to determine a frequency value (F1, F2) equal to the frequency of the first signals having maximum amplitude and as many amplitude values (A1-An) as there are sensors associated with that race; and b) processing the maximum amplitude values (A1-An) and frequency values (F1, F2) thus determined to calculate the forces and moments applied to the outer ring in real time, extrapolating them by means of a calibration map previously determined empirically through a non-linear regression function.