Abstract:
A control method configured to control the preload of a bearing includes estimating the preload on the bearing; comparing the estimated preload with a predetermined acceptance range; and correcting the preload on the bearing when the preload is outside the acceptance range.

Description:
PRIORITY CLAIM 
       [0001]    This application is a national stage application of PCT/IB2013/056443, filed on Aug. 6, 2013, which claims the benefit of and priority to Italian Patent Application No. MI2012A 001395, filed on Aug. 6, 2012, the entire contents of which are each incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    Certain known wind turbines for producing electric energy normally comprise a main frame that rotates about a vertical axis; a blade assembly, which comprises a hub fitted with at least two blades, and is connected to the main frame by at least one bearing to permit rotation of the blade assembly about an axis of rotation; and a rotary electric machine, which is rotated by the blade assembly, and comprises a stator connected to the main frame, and a rotor connected to the blade assembly. Normally, the stator comprises a tubular first active part, and the rotor comprises a tubular second active part facing, and separated by an air gap from, the tubular first active part. The efficiency of a rotary electric machine is known to be affected significantly by the size of the air gap: the smaller the air gap, the greater the efficiency of the electric machine. 
         [0003]    On direct-drive wind turbines, the blade assembly is connected rigidly to the rotor, and the bearing serves to support both the rotor and the blade assembly for rotation about the axis of rotation; and a fairly common practice is to employ one bearing designed to absorb radial and axial forces and tipping moments. Other wind turbine configurations employ two coaxial bearings. 
         [0004]    The bearings used between the blade assembly and main frame of wind turbines are normally rolling bearings. A rolling bearing comprises an outer ring and an inner ring; and at least one ring of rolling bodies equally spaced about the axis of rotation, between the outer and inner rings. On wind turbines, it is generally good practice to assemble the rolling bearings with a relatively small amount of interference between the inner ring on one side, the outer ring on the other side, and the rolling bodies between the inner ring and outer ring. In other words, the bearing can be assembled to achieve a relatively small amount of both radial and axial interference. Rolling bearings may normally be assembled with interference or clearance; and in the following description, the term ‘preload’ is used to describe both interference and clearance configurations. 
         [0005]    The set preload on the bearing at the installation stage may vary widely over time, depending on the temperature range at the wind turbine installation site, and on operating conditions, such as the heat generated by the rotary electric machine, friction in the bearing, and the efficiency of the cooling system. Changes in the preload of the bearing may produce relatively severe stress on the bearing, wear affecting the working life of the bearing, or slack which equally impairs the working life of the bearing and also alters the size of the air gap. Changes in the preload of the bearing therefore have a particularly harmful effect on the working life of the bearing and, in some situations, also on the efficiency of the electric machine. 
         [0006]    These drawbacks are further compounded by the current trend towards relatively large-diameter rotary electric machines. 
         [0007]    European Patent No. 2,290,250 discloses a method for controlling the temperature of a sleeve supporting two bearing at its opposite ends for a cartridge of drive-train of a geared wind turbine. 
         [0008]    European Patent No. 1,992,829 discloses a method for controlling the temperature of bearing in machine tool. 
         [0009]    Any one of these documents offers solutions that are not fully satisfactory for a direct drive wind turbine. 
       SUMMARY 
       [0010]    The present disclosure relates to a method of controlling the preload of a wind turbine bearing. 
         [0011]    It is an advantage of the present disclosure to provide a control method configured to control the preload of a wind turbine bearing, and which provides for achieving a relatively small air gap and, at the same time, ensuring a relatively long working life of the bearing. 
         [0012]    According to the present disclosure, there is provided a control method configured to control the preload of a wind turbine bearing, the method comprising the steps of estimating the preload on the bearing at least as a function of the temperature of the outer ring and the inner ring; comparing the estimated preload with a predetermined acceptance range; and correcting the preload on the bearing when the preload is outside the acceptance range; detecting the temperature of the outer ring; detecting the temperature of the inner ring; calculating the temperature difference between the outer ring and the inner ring; controlling the temperature of the outer ring and the inner ring as a function of the temperature difference between the outer ring and the inner ring so as to keep the preload within the predetermined acceptance range. 
         [0013]    In this way, it is possible to optimize both the working life of the bearing and the efficiency of the electric machine. 
         [0014]    In certain embodiments, the step of estimating the preload comprises calculating the preload on the basis of the structural, dimensional, and assembly characteristics, and the temperature of the bearing. 
         [0015]    In this way, it is possible to achieve a reliable estimate of the preload on the bearing. 
         [0016]    In certain embodiments, the step of correcting the preload on the bearing comprises directly or indirectly heating or cooling the outer ring and/or inner ring. 
         [0017]    This enables full active control of the preload of the bearing. 
         [0018]    In certain embodiments, the control method comprises determining the temperature of the outer ring and the inner ring, or of the supporting structures close to them. In this way, it is possible to implement a closed-cycle control algorithm. 
         [0019]    The temperature of the outer ring and the inner ring is, in certain embodiments, closed-cycle controlled by determining the temperature of the outer ring and the inner ring, or the temperature close to them, but open-cycle controls are not excluded. 
         [0020]    The present disclosure also relates to a program configured to control the preload of a bearing. 
         [0021]    According to the present disclosure, there is provided a computer program loadable directly into a memory of a control unit to perform the steps in the method according to the present disclosure when the program is implemented by the control unit. 
         [0022]    The program may also be stored in a mobile memory on a readable medium on which the program is stored. 
         [0023]    The present disclosure also relates to a control system configured to control the preload of a wind turbine bearing. 
         [0024]    According to the present disclosure, there is provided a control system configured to control the preload of a wind turbine bearing, the control system comprising a control unit configured to estimate the preload on the bearing at least as a function of the temperature of the outer ring and the inner ring; compare the estimated preload with a predetermined acceptance range; and correct the preload on the bearing when the preload is outside the acceptance range; at least one first sensor configured to detect the temperature of the outer ring; at least one second sensor configured to detect the temperature of the inner ring, wherein the control unit is configured to calculate the temperature difference between the outer ring and the inner ring and to control a first and a second control device to adjust the temperature of the outer ring and the inner ring respectively as a function of the temperature difference between the outer ring and the inner ring so as to keep the preload within the predetermined acceptance range. 
         [0025]    The control system provides for optimizing the working life of the bearing and the efficiency of the wind turbine electric machine relatively cheaply and relatively easily. In certain embodiments, the control unit is configured to calculate the preload on the basis of the structural, dimensional, and assembly characteristics, and the temperature of the bearing. 
         [0026]    The control unit is, in certain embodiments, programmable, has a memory in which to store bearing data, is configured to receive outside information, such as the detected temperatures of the outer ring and inner ring, and is configured to emit control signals to control a first and second control device. 
         [0027]    The control unit is also configured to emit alarm signals in the event of anomalous operating situations with respect to recorded history data. 
         [0028]    The present disclosure also relates to a wind turbine. 
         [0029]    According to the present disclosure, there is provided a wind turbine configured to produce electric energy, the wind turbine comprising a blade assembly rotatable about an axis of rotation; a rotary electric machine comprising a stator, and a rotor connected to the blade assembly; a bearing configured to support the blade assembly about the axis of rotation; and a control system configured to control the preload of the bearing and in accordance with the present disclosure. 
         [0030]    The above configuration provides for achieving a relatively small air gap, and improving the efficiency, of the rotary electric machine. 
         [0031]    Additional features and advantages are described in, and will be apparent from the following Detailed Description and the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    A non-limiting embodiment of the present disclosure will be described by way of example with reference to the attached drawings, in which: 
           [0033]      FIG. 1  shows a longitudinal section, with parts removed for clarity, of a wind turbine in accordance with the present disclosure; 
           [0034]      FIG. 2  shows a larger-scale longitudinal section, with parts removed for clarity, of the  FIG. 1  wind turbine equipped with a bearing preload control system in accordance with the present disclosure; 
           [0035]      FIG. 3  shows a larger-scale longitudinal section, with parts removed for clarity, of a detail of a variation of the present disclosure; 
           [0036]      FIG. 4  shows a longitudinal section, with parts removed for clarity, of a wind turbine in accordance with a further embodiment of the present disclosure; 
           [0037]      FIG. 5  shows a longitudinal section, with parts removed for clarity, of a wind turbine in accordance with a further embodiment of the present disclosure; and 
           [0038]      FIG. 6  shows a working life versus preload graph of the bearing. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Referring now to the example embodiments of the present disclosure illustrated in  FIGS. 1 to 6 , number  1  in  FIG. 1  indicates as a whole a wind turbine configured to produce electric energy. Wind turbine  1  is a direct-drive type. In the example shown, wind turbine  1  comprises a main frame  2 ; a rotary electric machine  3 ; and a blade assembly  4  which rotates about an axis of rotation A. Rotary electric machine  3  is located between main frame  2  and blade assembly  4  and, in addition to producing electric energy, serves to support blade assembly  4  and to transmit forces and moments induced by blade assembly  4  and rotary electric machine  3  itself to main frame  2 . 
         [0040]    In the example shown, main frame  2  is defined by a curved, tubular nacelle  5  comprising a circular end flange  6  for connection to rotary electric machine  3 ; an end flange  7  configured to house a pivot (not shown in the drawings) for connection to a vertical support (not shown in the drawings); and an opening  8  in the wall of nacelle  5 , through which to insert and remove relatively large component parts. In certain embodiments, opening  8  is substantially aligned with end flange  6 . 
         [0041]    Blade assembly  4  comprises a hub  9  connected to rotary electric machine  3 ; and a plurality of blades (not shown in the drawings). Hub  9  comprises a hollow member  10  configured to support the blades (not shown in the drawings); and a flange  11  for connection to rotary electric machine  3 . 
         [0042]    Rotary electric machine  3  extends about axis of rotation A, and is substantially tubular, so as to form a passage between the hollow main frame  2  and hollow hub  9 . 
         [0043]    Rotary electric machine  3  comprises a stator  12 ; a rotor  13  located inside stator  12  and which rotates with respect to stator  12  about axis of rotation A. Rotary electric machine  3  comprises a frame  14  configured to connect rotary electric machine  3  to main frame  2 , and configured to support blade assembly  4 , stator  12 , and rotor  13 . 
         [0044]    Frame  14  extends about axis of rotation A, and comprises a tubular structure  15 , which has a cylindrical face  16  and is configured to support a tubular active part  17  along cylindrical face  16 ; an annular flange  18  configured to connect rotary electric machine  3  to main frame  2  of wind turbine  1 ; and a ring  19  having an annular seat  20  for at least partly housing a bearing  21 . In the example shown, one bearing  21  supports blade assembly  4  and rotor  13  integral with blade assembly  4 . 
         [0045]    In other words, frame  14  forms part of tubular stator  12 , since tubular structure  15  forms part of tubular stator  12 . Accordingly, tubular stator  12  comprises tubular structure  15  and active part  17 . 
         [0046]    Tubular active part  17  is divided into a plurality of axial active segments  22 , each of which, in the example shown, has electric windings fitted to a ferromagnetic, substantially prismatic core extending predominantly parallel to axis of rotation A. 
         [0047]    Tubular structure  15  is cylindrical and extends about axis of rotation A. Annular flange  18  is coaxial with tubular structure  15  and smaller in diameter than cylindrical face  16 . And ring  19  is coaxial with tubular structure  15  and smaller in diameter than annular flange  18 . 
         [0048]    Annular flange  18  is located inside the end of tubular structure  15 , along axis of rotation A. 
         [0049]    Ring  19  is located inside the central area of tubular structure  15 , along axis of rotation A. 
         [0050]    Tubular structure  15 , annular flange  18  and ring  19  are connected rigidly to one another by arms  23  and  24 . More specifically, tubular structure  15  is connected to annular flange  18  by arms  23 , which extend predominantly radially with a relatively small axial component; and annular flange  18  is connected to ring  19  by arms  24 , which extend predominantly axially with a relatively small radial component. 
         [0051]    Each arm  23  comprises two plates  25  parallel to each other and to axis of rotation A. And similarly, each arm  24  comprises two plates  26  also parallel to each other and to axis of rotation A. 
         [0052]    Annular flange  18  has a seat  27  for connection to main frame  2  of wind turbine  1 . Frame  14  and main frame  2  are, in certain embodiments, connected by a bolted joint (not shown in the drawings) between annular flange  18  and end flange  6 , and by which the forces and moments induced by rotary electric machine  3  and blade assembly  4  are transmitted to main frame  2 . 
         [0053]    In certain embodiments, rotary electric machine  3 , (i.e., wind turbine  1 ) has only bearing  21  to withstand the radial and axial loads transmitted from tubular rotor  13  and blade assembly  4  to main frame  2 . 
         [0054]    With reference to  FIG. 2 , bearing  21  is a rolling bearing, comprises an outer ring  28  and an inner ring  29 , and is housed in annular seat  20  of ring  19 . More specifically, outer ring  28  is housed in annular seat  20 , and inner ring  29  is connected to tubular rotor  13 . Annular seat  20  has a step profile, with cylindrical faces alternating with annular supporting faces. More specifically, outer ring  28  of bearing  21  is housed inside annular seat  20  and locked in place by a lock ring  30  bolted to ring  19  and outer ring  28 . 
         [0055]    Tubular rotor  13  comprises a tubular structure  31  with a cylindrical face  32 ; a tubular active part  33 ; and a radial structure  34  located inside tubular structure  31  and connected to bearing  21 , more specifically to inner ring  29  of bearing  21 . In other words, radial structure  34  is fixed, on one side, to bearing  21  and, on the opposite side, to hub  9 , more specifically to flange  11  of hub  9 . 
         [0056]    Radial structure  34  is fixed to bearing  21  and hub  9  by two independently releasable bolted joints. Radial structure  34  is fixed using a lock ring  35  configured to partly house inner ring  29  of bearing  21 , and the end of radial structure  34  with flange  11  of hub  9 . 
         [0057]    Tubular active parts  17  and  33  are separated radially by an air gap T. 
         [0058]    One bolted joint comprises bolts, one of which, indicated  36  (in  FIGS. 1 and 2 ), engages lock ring  35 , radial structure  34  of rotor  13 , and flange  11  of hub  9 . The other bolted joint comprises bolts  37 , which only engage radial structure  34  of rotor  13 , and flange  11  of hub  9  ( FIG. 1 ). 
         [0059]    Radial structure  34  is also connectable by a joint, in particular a bolted joint, directly to ring  19 . Radial structure  34  is located close to a face  38  of ring  19 , and both radial structure  34  and ring  19  are configured to be connected integrally to each other. Radial structure  34  and ring  19  are connected to connect tubular rotor  13  directly to frame  14  when changing bearing  21 . 
         [0060]    Frame  14  has an emergency bearing  39  located along arms  24  and which is positioned contacting tubular rotor  13 —in the example shown, tubular structure  31 . 
         [0061]    Like active part  17 , active part  33  comprises axial active segments  40 , each of which, in the example shown, has permanent magnets fitted to respective magnetic guides, is prismatic in shape, and extends predominantly parallel to axis of rotation A. 
         [0062]    Tubular rotary electric machine  3  communicates directly with hollow hub  9 , and is traversed by cooling air, which is indicated by arrows F, is appropriately blown inside rotary electric machine  3 , and serves mainly to cool active parts  17  and  33 . Cooling air F sweeps over the area where bearing  21  is assembled, and in particular the inner ring  29  area. To mitigate the effect of cooling air F, wind turbine  1  comprises an insulating cover  41  configured to insulate the area swept by cooling air F. In the example shown, insulating cover  41  is tubular and applied to lock ring  35 . More specifically, insulating cover  41  is also shaped to guide the flow of cooling air F. 
         [0063]    In addition to outer ring  28  and inner ring  29 , bearing  21  also comprises rolling bodies  42  arranged in two rings. More specifically, inner ring  29  comprises two adjacent half-rings  29 A and  29 B. Wind turbine  1  comprises a control system  43  configured to control the preload of bearing  21 . The term ‘preload’ is a general term relating to interference or clearance between outer ring  28 , inner ring  29  and rolling bodies  42  of bearing  21 . The preload is divided into a radial preload and an axial preload with reference to axis of rotation A. On wind turbines, the bearing is normally assembled with interference. In the example shown, the preload is set at the assembly stage, by hot-fitting, with a relatively small amount of interference, outer ring  28  inside seat  20  on ring  19 , and inner ring  29  inside a seat on lock ring  35 . 
         [0064]    Lock ring  35  is also tightened to radial structure  34  by bolts  36 . Tightening bolts  36  brings half-rings  29 A and  29 B closer together to produce the axial preload. 
         [0065]    Control system  43  comprises a control device  44  configured to control outer ring  28 ; a control device  45  configured to control inner ring  29 ; a temperature sensor  46  configured to detect the temperature of outer ring  28 ; a temperature sensor  47  configured to detect the temperature of inner ring  29 ; and a control unit  48  configured to control control devices  44  and  45  on the basis of the detected temperatures of outer ring  28  and inner ring  29 . 
         [0066]    Outer ring  28  is the stationary part of bearing  21 , while inner ring  29  is integral with rotor  13  and, in use, rotates about axis of rotation A with respect to outer ring  28 . 
         [0067]    Control device  44  comprises a thermostat  49 ; a heat exchanger  50  close to outer ring  28 ; and connecting lines  51  between thermostat  49  and heat exchanger  50 . 
         [0068]    Similarly, control device  45  comprises a thermostat  52 ; a heat exchanger  53  close to inner ring  29 ; connecting lines  54  between thermostat  52  and heat exchanger  53 ; and a rotary distributor  55  located along connecting lines  54  to connect the stationary part to the rotary part of control device  45 . 
         [0069]    In the example shown, heat exchanger  53  is located along the inner face of lock ring  35 . 
         [0070]    Control devices  44  and  45  are, in certain embodiments, electric, and heat exchangers  50  and  53  are electric resistors located close to, and, in certain embodiments, coiled about, outer ring  28  and inner ring  29 , respectively. 
         [0071]    In a variation of the present disclosure, control devices  44  and  45  are liquid types, so heat exchangers  50  and  53  can cool as well as heat outer ring  28  and inner ring  29 . 
         [0072]    Bearing  21  is selected on the basis of its capacity and other parameters, including operating temperature. And control system  43  provides for maintaining the temperature of outer ring  28  and inner ring  29  so as to keep the preload within a predetermined acceptance range I. 
         [0073]    The algorithm implemented by control system  43  is substantially based on the characteristics and the assembly conditions of bearing  21 , on the thermal deformation of bearing  21  as a function of the temperature of outer ring  28  and inner ring  29 , and on the variations in preload as a function of said thermal deformation. Given this data, it is possible to calculate the preload as a function of the temperature of outer ring  28  and inner ring  29 . And the calculated preload is compared with the predetermined preload acceptance range I shown in  FIG. 6 . As shown in  FIG. 6 , the preload acceptance range I (x axis) is chosen to ensure a relatively long predicted working life (y axis) of bearing  21 . 
         [0074]    Control unit  48  is programmable, and comprises a memory in which to store the characteristics of bearing  21 . Control unit  48  is configured to calculate the deformation of bearing  21  on the basis of the detected temperatures of outer ring  28  and inner ring  29 , and/or the difference between the detected temperatures of outer ring  28  and inner ring  29 . Control unit  48  is configured to calculate the preload on the basis of the thermal deformation of outer ring  28  and inner ring  29 ; and to compare the calculated preload with preload acceptance range I. If the calculated preload does not fall within acceptance range I, the control unit commands thermostats  49  and  52  to heat and/or cool outer ring  28  and/or inner ring  29  to bring the preload back within acceptance range I. 
         [0075]    Control unit  48  is configured to memorize the temperature data of outer ring  28  and inner  29  together with data detected and memorized by the control unit controlling wind turbine  1  as a whole, so as to determine any anomalous behaviour of bearing  21 . For example, for a given or designated external temperature, cooling system efficiency, wind speed, and blade angle, overheating of bearing  21  may be detected, and which may be considered anomalous in the light of other operating conditions. In which case, control unit  48  is configured to emit an alarm signal. 
         [0076]    In relatively very cold climates, and when wind turbine  1  is re-started, the temperatures of outer ring  28  and inner ring  29  are below the optimum operating parameters of bearing  21 , so both rings must be heated. 
         [0077]    Other environmental and operating conditions make it necessary to heat outer ring  28  and inner ring  29  differently. This differential temperature of outer ring  28  and inner ring  29  is made possible by control system  43 . 
         [0078]    In the  FIG. 3  variation, heat exchanger  53  is located between lock ring  35  and inner ring  29  of bearing  21 . 
         [0079]    Number  56  in  FIG. 4  indicates a wind turbine configured to produce electric energy. Wind turbine  56  is a direct-drive type and, in the example shown, comprises a rotary electric machine  57 ; and a blade assembly  58  which rotates about an axis of rotation A. In addition to producing electric energy, rotary electric machine  57  also serves to support blade assembly  58  and to transmit forces and moments induced by blade assembly  58  and rotary electric machine  57  itself to the main frame (not shown in the drawings) of wind turbine  56 . 
         [0080]    Blade assembly  58  comprises a hub  59  connected to rotary electric machine  57 ; and a plurality of blades (not shown in the drawings). Hub  59  comprises a hollow member  60  configured to support the blades (not shown in the drawings); and a flange  61  for connection to rotary electric machine  57 . 
         [0081]    Rotary electric machine  57  is substantially tubular, so as to form a space for access to hollow hub  59 . 
         [0082]    Rotary electric machine  57  comprises a stator  62 ; and a rotor  63  located inside stator  62 . Stator  62  comprises a ring  64  having an annular seat  65  for at least partly housing a bearing  66 ; and a radial structure  67  configured to connect ring  64  to a tubular structure (not shown in the drawings). In the example shown, one bearing  66  supports blade assembly  58  and rotor  63  integral with blade assembly  58 . 
         [0083]    Rotor  63  comprises a ring  68  with an annular seat  69  configured to house bearing  66 ; and a radial structure  70  configured to connect ring  68  to a further tubular structure (not shown in the drawings). 
         [0084]    In certain embodiments, rotary electric machine  57  (i.e., wind turbine  56 ) has only bearing  66  to withstand radial and axial forces and tipping moments. Bearing  66  is a rolling bearing and comprises an outer ring  71  and an inner ring  72 . In the example shown, bearing  66  is a rolling bearing with two rings of rolling bodies  73 —in the example shown, rollers. More specifically, outer ring  71  is housed in annular seat  65 , and inner ring  72  is housed in annular seat  69  on ring  68  of rotor  63 . Outer ring  71  of bearing  66  is locked inside annular seat  65  by a lock ring  74  bolted to ring  64  and outer ring  71 . 
         [0085]    Inner ring  72  comprises two half-rings  72 A and  72 B, which are arranged axially adjacent inside seat  69 , and are locked axially by a lock ring  75  and by a bolted joint by which to set the axial preload. 
         [0086]    Wind turbine  56  comprises a control system  43  as described with reference to  FIG. 2 . Heat exchanger  50  is housed inside grooves formed in ring  64  of stator  62 , at annular seat  65 , so as to directly contact outer ring  71 . Likewise, heat exchanger  53  is housed inside grooves formed in ring  68  of rotor  63 , at annular seat  69 , so as to directly contact inner ring  72 . 
         [0087]    Temperature sensor  46  is located inside a space in ring  64 , between ring  64  and outer ring  71 , and, in certain embodiments, along a front face of outer ring  71 , at a given or designated distance from heat exchanger  50 . And likewise, temperature sensor  47  is located inside a space in ring  68 , such as between ring  68  and inner ring  72 , and in certain embodiments, facing a front face of inner ring  72 , and at a given or designated distance from heat exchanger  53 . 
         [0088]    Number  76  in the  FIG. 5  embodiment indicates an electric energy producing wind turbine. Wind turbine  76  is a direct-drive type and, in the example shown, comprises a rotary electric machine  77 ; and a blade assembly  78  which rotates about an axis of rotation A. In addition to producing electric energy, rotary electric machine  77  also serves to support blade assembly  78  and to transmit forces and moments induced by blade assembly  78  and rotary electric machine  77  itself to the main frame  79  of wind turbine  76 . 
         [0089]    Blade assembly  78  comprises a hollow hub  80  connected to rotary electric machine  77 ; and a plurality of blades (not shown in the drawings). Hub  80  comprises a flange  81  for connection to rotary electric machine  77 . 
         [0090]    Rotary electric machine  77  extends about axis of rotation A, and is substantially tubular to form a space for access to hollow hub  80 . 
         [0091]    Rotary electric machine  77  comprises a stator  82 ; and a rotor  83  located inside stator  62 , and which rotates about axis of rotation A with respect to stator  82 . Stator  82  comprises a tubular structure  84  having a cylindrical face  85  and configured to support a tubular active part  86  along cylindrical face  85 . 
         [0092]    Rotor  83  comprises a tubular structure  87  with a cylindrical face  88 ; and a tubular active part  89  fitted to cylindrical face  88  of tubular structure  87 . 
         [0093]    Tubular structures  84  and  87  are connected in rotary manner by two bearings  90  and  91  located at opposite ends of tubular structures  84  and  87 , which have reinforcing rings at the ends, and assembly rings. Each bearing  90 ,  91  comprises an outer ring  92 , an inner ring  93 , and a ring of rolling bodies  94 . Bearing  90  is stressed more than bearing  91 , is preloaded with interference, and is actively controlled by control system  43 . In this case, the grooves housing heat exchangers  50  and  53  are formed in tubular structures  84  and  87 , at end seats of bearings  90  and  91 . 
         [0094]    Clearly, changes may be made to the control method and system and the wind turbine according to the present disclosure without, however, departing from the protective scope of the accompanying Claims. In particular, the control method and system described and claimed also apply to wind turbines with overgears and with structures other than those described with reference to the attached drawings, and may also be used to advantage for controlling bearings other than those described. Accordingly, various changes and modifications to the presently disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.