Abstract:
A yaw brake mechanism is described for maintaining a yawing structure, such as a nacelle of a fluid turbine, at a desired orientation or azimuthal heading about a reference or yaw axis. The yaw brake mechanism uses one or more rotor locks and one or more receptacles that cooperate with one another to achieve the locking function. One of the rotor locks is actuatable so that a portion thereof can be engaged in one of the receptacles to lock the yawing structure. The number of rotor locks and receptacles can be selected to allow the yawing structure to achieve any azimuth heading around the full 360 degrees of the yaw axis with various degrees of accuracy. The yaw brake mechanism allows the yawing structure to maintain multiple headings while being subjected to extreme moment and force loads in a low mass, low height, low cost solution.

Description:
FIELD 
       [0001]    This technical disclosure relates to a yawing structure and a yaw brake mechanism for maintaining the yawing structure at a desired azimuthal heading. 
       BACKGROUND 
       [0002]    Yawing structures, including certain fluid turbines, may require the ability to achieve different azimuth headings throughout their deployment. For example, in the case of certain fluid turbines such as tidal turbines, water turbines, or wind turbines, the fluid flow heading is often variable, and the rotor of the turbine needs to be oriented in the proper orientation relative to the flow of the fluid in order for the fluid turbine to efficiently harness power to maximize power production. 
         [0003]    Existing solutions that are currently employed as yaw brake mechanisms include disc brakes and motor brakes. Utilization of disc brakes as a yaw braking mechanism follows the same principle as a car&#39;s disc brake system, but on a much larger scale. Utilizing disc brakes requires a large number of disc brakes to accommodate the high torque. This results in a heavy, tall, and costly braking mechanism. 
         [0004]    Motor brakes employ a low torque brake within the yaw drive powertrain system. The brake&#39;s low torque is multiplied by the use of a high gear ratio gearbox to create a large torque at the pinion to slew bearing interface. Using multiple powertrains further increases the braking torque available at the slew bearing. 
         [0005]    In addition, it is known to use a single rotor lock mechanism between the rotor hub and nacelle interface of a wind turbine for hub lock out (i.e. prevent rotation of the rotor hub relative to the nacelle) during maintenance. 
       SUMMARY 
       [0006]    A yaw brake mechanism is described for maintaining a yawing structure at a desired orientation or azimuthal heading about a reference axis. In one embodiment, the yaw brake mechanism allows the yawing structure to achieve and subsequently maintain multiple headings while being subjected to extreme moment and force loads in a low mass, low height, low cost solution. 
         [0007]    As used herein, the term yawing structure refers to any structure where the orientation of the structure relative to a reference axis can be selectively altered and where the yawing structure can be held or locked at a particular orientation relative to the reference axis. 
         [0008]    In one non-limiting example, a yawing structure can be a structure that is rotatable about a yaw axis, which can be a vertical or near vertical axis, and locked in a particular orientation about the yaw axis. 
         [0009]    Examples of yawing structures that are intended to be encompassed within this disclosure include, but are not limited to, nacelles of tidal turbines, water turbines or wind turbines. The nacelle is rotatable about a yaw axis relative to a tower on which the nacelle is rotatably supported. The nacelle rotatably supports a rotor that in use is driven by a fluid, such as water or air, flowing past the rotor in order to generate electrical energy and/or produce mechanical energy from the rotation of the rotor. A yaw drive mechanism is included that is used to selectively cause rotation of the nacelle to a desired orientation or azimuthal heading about the yaw axis. In addition, a yaw brake mechanism is provided that is selectively actuatable to lock the nacelle at the desired orientation. In one described embodiment, the yaw brake mechanism provides a means of achieving and subsequently maintaining multiple azimuth headings. 
         [0010]    In one embodiment, the yaw brake mechanism has at least one rotor lock and at least one receptacle that can cooperate with one another to achieve the locking function. In another embodiment described herein, the yaw brake mechanism has a plurality of rotor locks and a plurality of receptacles that can cooperate with one another to achieve the locking function. When multiple rotor locks and receptacles are used, one of the rotor locks is actuatable to an engaged condition so that a portion thereof is engaged in one of the receptacles to lock the yawing structure. In one embodiment, a single rotor lock is capable of countering the full torque of the yawing structure. In other embodiments, more than one rotor lock can be simultaneously engaged with the receptacles. In one non-limiting example, the number of rotor locks and receptacles can be selected to allow the yawing structure to achieve any azimuth heading around the full 360 degrees of rotation with less than about ±1.0 degree accuracy. In another non-limiting example, eight rotor locks and twenty-five receptacles can be used. 
         [0011]    In one example, a yaw brake mechanism of a yawing structure that is rotatably mounted on a non-rotatable structure and that is rotatable about a yaw axis of the non-rotatable structure can include at least one rotor lock that is actuatable between an engaged condition and a disengaged condition. A lock plate can cooperate with the at least one rotor lock for fixing the yawing structure in a desired orientation about the yaw axis. The lock plate can include at least one receptacle that can receive a portion of the at least one rotor lock therein when the at least one rotor lock is actuated to the engaged condition. The lock plate and the at least one rotor lock are positioned relative to each other whereby the portion of the at least one rotor lock is disposed within the at least one receptacle of the lock plate when the at least one rotor lock is actuated to the engaged condition thereby preventing rotation of the yawing structure about the yaw axis, and the portion of the at least one rotor lock is removed from the at least one receptacle of the lock plate when the at least one rotor lock is actuated to the disengaged condition thereby permitting rotation of the yawing structure about the yaw axis. 
         [0012]    In another example, a fluid turbine described herein can include a tower having a yaw axis, a nacelle rotatably mounted on the tower and rotatable about the yaw axis to change an orientation of the nacelle about the yaw axis, a yaw drive mechanism for rotating the nacelle about the yaw axis, a rotor rotatably mounted on the nacelle for rotation about a rotation axis, and a yaw brake mechanism for fixing the orientation of the nacelle about the yaw axis. The yaw brake mechanism can include at least one rotor lock mounted to either the nacelle or the tower that is actuatable between an engaged condition and a disengaged condition. A lock plate is provided that cooperates with the at least one rotor lock for fixing the nacelle in a desired orientation about the yaw axis, the lock plate mounted to either the tower or the nacelle. The lock plate includes at least one receptacle that can receive a portion of the at least one rotor lock therein when the at least one rotor lock is actuated to the engaged condition. In addition, the lock plate and the at least one rotor lock are positioned relative to each other whereby the portion of the at least one rotor lock is disposed within the at least one receptacle of the lock plate when the at least one rotor lock is actuated to the engaged condition thereby preventing rotation of the nacelle about the yaw axis and the portion of the at least one rotor lock is removed from the at least one receptacle of the lock plate when the at least one rotor lock is actuated to the disengaged condition thereby permitting rotation of the nacelle about the yaw axis. 
     
    
     
       DRAWINGS 
         [0013]      FIG. 1  is a perspective side view of a portion of a turbine that utilizes the yaw brake mechanism described herein, with portions of the turbine removed or made transparent in order to illustrate the concepts of the yaw brake mechanism. 
           [0014]      FIG. 2  is an upper perspective view of a yaw drive mechanism together with the yaw brake mechanism contained in a region between the nacelle and the tower of the turbine of  FIG. 1 . 
           [0015]      FIG. 3  is a view similar to  FIG. 2  with a rotating plate of the yaw drive mechanism removed to better illustrate the components of the yaw drive mechanism and the yaw brake mechanism. 
           [0016]      FIG. 4  is a cross-sectional view taken along line  4 - 4  of  FIG. 2 . 
           [0017]      FIG. 5  is an upper perspective view of another embodiment of a yaw drive mechanism and a yaw brake mechanism. 
           [0018]      FIG. 6  is a cross-sectional view taken along line  6 - 6  of  FIG. 5 . 
           [0019]      FIG. 7  illustrates a hydraulic system of the yaw brake mechanism for actuating the rotor locks. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    A yaw brake mechanism, which can also be referred to as a yaw holding brake, is described for maintaining a yawing structure at a desired orientation or azimuthal heading about a reference axis. A yawing structure can be any structure where the orientation of the structure relative to the reference axis can be selectively altered and where one wishes to hold or lock the yawing structure at a particular orientation relative to the reference axis. 
         [0021]    For sake of convenience, the yawing structure will be described below as, and is illustrated herein as, a fluid driven turbine, in particular a nacelle of the fluid driven turbine. The fluid driven turbine can include, but is not limited to, a tidal turbine, a water turbine, or a wind turbine. The nacelle is rotatable about a yaw axis which, for sake of convenience, will be described as being a vertical or near vertical axis. However, the yaw brake concepts described herein can be applied to other yawing structures that are rotatable about yaw axes that are not vertical or near vertical. 
         [0022]    With reference to  FIG. 1 , a portion of a fluid driven turbine  10  is illustrated. The turbine  10  includes a nacelle  12  which is rotatably mounted at an upper end of a tower  14 , via a yaw drive mechanism  30  described below, for rotation relative to the tower  14  about a yaw axis A-A. In  FIG. 1 , the nacelle  12 , which may also be referred to as a housing, is illustrated as being transparent in order to allow the interior components within the nacelle  12  to be viewed. In the actual turbine  10 , the nacelle  12  would not be transparent. The tower  14  can be fixedly mounted in any manner so that it does not rotate. For example, the tower  14  can be mounted directly or indirectly in or on the ground in the case of a wind turbine; the tower  14  can be mounted directly or indirectly in or on a sea floor or the bottom of another body of water in the case of a water or tidal turbine. 
         [0023]    In one embodiment, the yaw axis A-A can extend substantially vertically. In other embodiments, the yaw axis A-A can be inclined at an angle to vertical. The yaw axis A-A can be inclined at any angle to vertical. For example, in one non-limiting embodiment, the yaw axis can be inclined ±4 degrees from vertical. 
         [0024]    The nacelle  12  includes a first end  16 , which can be a forward or front end, and a second end  18 , which can be a back or rear end. A rotor  20  is rotatably mounted at the first end  16  for rotation about a rotation axis B-B. In one embodiment, the rotation axis B-B can extend substantially horizontally. In other embodiments, the rotation axis B-B can be inclined at an angle to horizontal. 
         [0025]    In the illustrated example, the rotor  20  includes a plurality of blades (not shown) that are detachably mounted to blade mounts  22  that extend generally radially from the rotor  20 . In the illustrated example, there are three blade mounts  22  and therefore three blades. However, a larger or smaller number of blade mounts and blades can be used. The blade mounts  22  and the blades mounted thereto can be fixed pitch, or the blade mounts  22  and the blades fixed thereto can be mounted so as to permit pitch variation by rotating about an axis C-C of the blade mounts  22  and blades. In the case of variable pitch blades, a pitch change mechanism (not shown in detail) can be provided within the rotor  20 . As would be well understood by a person of ordinary skill in the art, the rotor  20  is designed to be rotated about the rotation axis B-B as a result of a fluid, such as water or air, flowing past the blades thereof as illustrated by the arrows F in  FIG. 1 . 
         [0026]    With continued reference to  FIG. 1 , a gearbox  24  and a generator  26  are mounted at the second end  18 . A shaft  28  that extends through the nacelle  12  connects the rotor  20  to the gearbox  24  so that rotation of the rotor  20  is transferred to the gearbox  24  which in turn results in electricity generation in the generator  26 . The detailed construction and operation of the rotor  20 , the gearbox  24  and the generator  26  are well known to those of ordinary skill in the art and are not further described herein. 
         [0027]    Between the nacelle  12  and the tower  14 , the yaw drive mechanism  30  is provided that is configured to rotate the nacelle  12  about the yaw axis A-A relative to the tower  14 . The yaw drive mechanism  30  changes the azimuthal heading or orientation of the nacelle  12  and the rotor  20  mounted thereon about the yaw axis A-A in order to orient the rotor  20  at the optimal heading relative to the fluid flow F which can change direction. The yaw drive mechanism  30  can have any construction that is suitable for achieving rotation of the nacelle  12  about the yaw axis A-A. The specific construction and operation of yaw drive mechanisms is well known in the art. 
         [0028]    With reference to  FIGS. 2-4 , details of the yaw drive mechanism  30  are illustrated. The yaw drive mechanism  30  described herein is an example only and other yaw drive mechanism constructions can be used.  FIGS. 2-4  illustrate the region between the nacelle  12  and the tower  14  of the turbine  10 . In this example, the yaw drive mechanism  30  includes a plurality of yaw powertrains  32 , for example three yaw powertrains  32 , each of which includes a drive motor  34  and associated gearing driven by the respective drive motor  34 . The powertrains  32  can work together, in any combination thereof, or individually to drive the rotation of the nacelle  12 . 
         [0029]    As best seen in  FIGS. 3 and 4 , each powertrain  32  drives a pinion gear  36 . The pinion gears  36  are engaged with gear teeth  38  formed on an inner periphery of a slew bearing  40 . The slew bearing  40  includes a stationary or fixed inner bearing race  42  that is mounted on a base plate  44  that is fixed to the tower  14  (connection not shown). In this embodiment, the gear teeth  38  can be integrally formed on the inner bearing race  42  so that the gear teeth  38  and the inner bearing race  42  form a unitary or single-piece construction. The slew bearing  40  also includes a rotatable outer bearing race  46  that is rotatable about, and relative to, the inner bearing race  42 . 
         [0030]    With reference to  FIGS. 2 and 4 , a rotatable plate  48  is fixed to the top of the outer bearing race  46 . The rotatable plate  48  is illustrated as being transparent in  FIG. 3  in order to show components underneath the rotatable plate  48 . The yaw powertrains  32  are mounted on the rotatable plate  48  with the drive motors  34  on an upper side of the rotatable plate  48  and the pinion gears  36  on the opposite side of the rotatable plate  48 . In addition, the rotatable plate  48  is fixed to the nacelle  12 . 
         [0031]    The yaw drive mechanism  30  operates as follows. One or more of the motors  34  is actuated in order to rotate the respective pinion gear  36 . Since the pinion gear(s)  36  is engaged with the teeth  38  of the inner bearing race  42  which is fixed, the plate  48  and the outer bearing race  46 , and the nacelle  12  connected thereto, are rotated about the yaw axis A-A. 
         [0032]    Once the nacelle  12  is rotated to the correct azimuthal heading, a yaw brake mechanism  50  is used to hold or lock the nacelle  12  at the desired azimuthal heading. In one embodiment, the yaw brake mechanism  50  can include a single rotor lock  52  and a single receptacle  54 , both described further below, that cooperate with one another to achieve the locking function. The single rotor lock  52  and the single receptacle  54  can lock the nacelle  12  at a single azimuthal heading. However, it is possible to mount either or both of the single rotor lock  52  and the receptacle  54  in a manner to permit the relative locations of the rotor lock  52  and the receptacle  54  to be selectively altered, in which case the nacelle  12  could be locked at other azimuthal headings depending upon the relative locations of the rotor lock  52  and the receptacle  54 . 
         [0033]    In another embodiment described in further detail below, the yaw brake mechanism  50  includes a plurality of rotor locks  52  and a plurality of receptacles  54  that cooperate with at least one of the rotor locks  52  to achieve the locking function. One of the rotor locks  52  is actuatable so as to be engageable in one of the receptacles  54  to lock the nacelle  12  at the desired azimuthal heading. One of the rotor locks  52  is engageable with one of the receptacles  54  to achieve locking so that the single rotor lock  52  is capable of countering the full torque of the nacelle  12 . 
         [0034]    In one embodiment, there are at least two rotor locks  52  and at least two receptacles  54 . In another embodiment, the number of the receptacles  54  is greater than the number of the rotor locks  52 . In one embodiment described further below, the number of the rotor locks  52  and the receptacles  54  can be selected to allow the nacelle  12  to achieve any azimuth heading around the full 360 degrees about the yaw axis A-A with less than about ±1.0 degree accuracy. For example, in one embodiment, there can be eight of the rotor locks  52  and twenty-five of the receptacles  54  to achieve this full range of azimuth headings and accuracy. 
         [0035]    The yaw brake mechanism  50  with multiple rotor locks  52  and multiple receptacles  54  will be described with reference to  FIGS. 2-4 . The rotor locks  52  are actuatable between an engaged (or first or extended) condition where a portion thereof is disposed in one of the receptacles  54  and a disengaged (or second or retracted) condition where a portion thereof is not disposed in one of the receptacles  54 . In the illustrated example, the rotor locks  52  are illustrated as including hydraulic actuated pistons  56  that are actuatable in a direction substantially parallel to the yaw axis A-A. Each rotor lock  52  is actuatable between an engaged (or first or extended) condition where the piston  56  thereof is disposed in one of the receptacles  54  and a disengaged (or second or retracted) condition where the piston  56  thereof is not disposed in one of the receptacles  54 . Referring to  FIG. 4 , the rotor lock  52  on the left side of  FIG. 4  is shown as being actuated to the engaged condition where the piston  56  thereof is disposed in one of the receptacles  54 , while the rotor lock  52  on the right side of  FIG. 4  is shown as being actuated to the disengaged condition where the piston  56  thereof is not disposed in one of the receptacles  54 . The rotor locks  52  can have structures other than the pistons  56  that can be selectively disposed within the receptacles  54 . 
         [0036]      FIG. 2  illustrates the rotor locks  52  as being separated into two groups of rotor locks  52   a ,  52   b . Each group includes a plurality of the rotor locks  52 . The rotor locks  52  are mounted in respective raised areas  60   a ,  60   b  formed on and projecting upward from the upper surface of the plate  48 . However, the rotor locks  52  can be separated into any number of groups, with an equal or unequal number of rotor locks in each group. In addition, in another embodiment, the rotor locks  52  can be arranged in a single group similar to that discussed below with respect to  FIGS. 5 and 6 . 
         [0037]    As shown in  FIGS. 3 and 4 , the receptacles  54  are formed in an upper surface of the inner bearing race  42  facing the bottom surface of the plate  48 . In this embodiment, the receptacles  54  and the inner bearing race  42  are integrally formed with one another forming a unitary or single-piece construction. The inner bearing race  42  forms a lock plate where the receptacles  54  cooperate with the rotor locks  52  for fixing the nacelle  12  in a desired azimuth heading about the yaw axis. In particular, a receptacle  54  can receive the piston  56  of one of the rotor locks  52  therein when the rotor lock  52  is actuated to the engaged condition thereby preventing rotation of the nacelle  12  about the yaw axis and the piston  56  of the rotor lock  52  is removed from the receptacle  54  of the lock plate when the rotor lock  52  is actuated to the disengaged condition thereby permitting rotation of the nacelle  12  about the yaw axis. In an embodiment, the receptacles  54  can be provided in two or more rings or plates that form the inner bearing race  42  or are separate from the inner bearing race  42 . 
         [0038]    As best seen in  FIGS. 3 and 4 , the receptacles  54  comprise generally circular indentations formed in the inner bearing race  42  but do not extend through the inner bearing race  42 . In another embodiment, the receptacles  54  can extend completely through the inner bearing race  42 . The receptacles  54  and the ends of the pistons  56  of the rotor locks  52  to be disposed therein can be shaped to facilitate entry and release of the pistons  56  of the rotor locks  52  into and from the receptacles  54 . For example, an end  62  of each piston  56  of the rotor locks  52  can be tapered. In addition, the interior of the receptacles  54  can have a corresponding tapered shape, for example by tapering the side walls of the receptacles  54  or installing a tapered liner  64  in each receptacle  54 . In the illustrated embodiment, each receptacle  54  has an axis that is substantially parallel to the yaw axis A-A, and the pistons  56  of the rotor locks  52  are actuatable in a direction that is substantially parallel to the yaw axis A-A. However, in another embodiment, the receptacles  54  and the pistons  56  of the rotor locks  52  can be arranged such that their axes are not parallel to the yaw axis A-A. 
         [0039]    As indicated above, a selected one of the pistons  56  of the rotor locks  52  can be actuated to a position where the end  62  of the piston is disposed in one of the receptacles  54  to lock the azimuthal heading of the nacelle  12 . By providing multiple rotor locks  52  and multiple receptacles  54 , the range of angles at which the nacelle  12  can be locked is increased. For example, in the illustrated embodiment with eight of the rotor locks  52  and twenty-five of the receptacles  54 , the nacelle  12  can achieve numerous azimuth headings around the full 360 degrees about the yaw axis A-A with less than about ±1.0 degree accuracy. The following table illustrates angles that are achievable by the nacelle  12  in the illustrated embodiment. 
         [0040]    In the table below, the rotor locks  52  are labeled A to H in  FIG. 3 . In addition, assuming the piston of the rotor lock A in  FIG. 3  is engaged in receptacle  1 , the remaining receptacles are then labeled consecutively up to 25 in a clockwise direction. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 ROTOR LOCK 
               
             
          
           
               
                   
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
                 G 
                 H 
               
               
                   
                   
               
             
          
           
               
                 RE- 
                 1 
                 0 
                 343.8 
                 327.6 
                 311.4 
                 180 
                 163.8 
                 147.6 
                 131.4 
               
               
                 CEP- 
                 2 
                 14.4 
                 358.2 
                 342 
                 325.8 
                 194.4 
                 178.2 
                 162 
                 145.8 
               
               
                 TACLE 
                 3 
                 28.8 
                 12.6 
                 356.4 
                 340.2 
                 208.8 
                 192.6 
                 176.4 
                 160.2 
               
               
                   
                 4 
                 43.2 
                 27 
                 10.8 
                 354.6 
                 223.2 
                 207 
                 190.8 
                 174.6 
               
               
                   
                 5 
                 57.6 
                 41.4 
                 25.2 
                 9 
                 237.6 
                 221.4 
                 205.2 
                 189 
               
               
                   
                 6 
                 72 
                 55.8 
                 39.6 
                 23.4 
                 252 
                 235.8 
                 219.6 
                 203.4 
               
               
                   
                 7 
                 86.4 
                 70.2 
                 54 
                 37.8 
                 266.4 
                 250.2 
                 234 
                 217.8 
               
               
                   
                 8 
                 100.8 
                 84.6 
                 68.4 
                 52.2 
                 280.8 
                 264.6 
                 248.4 
                 232.2 
               
               
                   
                 9 
                 115.2 
                 99 
                 82.8 
                 66.6 
                 295.2 
                 279 
                 262.8 
                 246.6 
               
               
                   
                 10 
                 129.6 
                 113.4 
                 97.2 
                 81 
                 309.6 
                 293.4 
                 277.2 
                 261 
               
               
                   
                 11 
                 144 
                 127.8 
                 111.6 
                 95.4 
                 324 
                 307.8 
                 291.6 
                 275.4 
               
               
                   
                 12 
                 158.4 
                 142.2 
                 126 
                 109.8 
                 338.4 
                 322.2 
                 306 
                 289.8 
               
               
                   
                 13 
                 172.8 
                 156.6 
                 140.4 
                 124.2 
                 352.8 
                 336.6 
                 320.4 
                 304.2 
               
               
                   
                 14 
                 187.2 
                 171 
                 154.8 
                 138.6 
                 7.2 
                 351 
                 334.8 
                 318.6 
               
               
                   
                 15 
                 201.6 
                 185.4 
                 169.2 
                 153 
                 21.6 
                 5.4 
                 349.2 
                 333 
               
               
                   
                 16 
                 216 
                 199.8 
                 183.6 
                 167.4 
                 36 
                 19.8 
                 3.6 
                 347.4 
               
               
                   
                 17 
                 230.4 
                 214.2 
                 198 
                 181.8 
                 50.4 
                 34.2 
                 18 
                 1.8 
               
               
                   
                 18 
                 244.8 
                 228.6 
                 212.4 
                 196.2 
                 64.8 
                 48.6 
                 32.4 
                 16.2 
               
               
                   
                 19 
                 259.2 
                 243 
                 226.8 
                 210.6 
                 79.2 
                 63 
                 46.8 
                 30.6 
               
               
                   
                 20 
                 273.6 
                 257.4 
                 241.2 
                 225 
                 93.6 
                 77.4 
                 61.2 
                 45 
               
               
                   
                 21 
                 288 
                 271.8 
                 255.6 
                 239.4 
                 108 
                 91.8 
                 75.6 
                 59.4 
               
               
                   
                 22 
                 302.4 
                 286.2 
                 270 
                 253.8 
                 122.4 
                 106.2 
                 90 
                 73.8 
               
               
                   
                 23 
                 316.8 
                 300.6 
                 284.4 
                 268.2 
                 136.8 
                 120.6 
                 104.4 
                 88.2 
               
               
                   
                 24 
                 331.2 
                 315 
                 298.8 
                 282.6 
                 151.2 
                 135 
                 118.8 
                 102.6 
               
               
                   
                 25 
                 345.6 
                 329.4 
                 313.2 
                 297 
                 165.6 
                 149.4 
                 133.2 
                 117 
               
               
                   
               
             
          
         
       
     
         [0041]      FIGS. 5 and 6  illustrate another embodiment of a yaw drive mechanism  100 .  FIGS. 5-6  illustrate the region between the nacelle (not shown) and the tower (not shown) of the turbine which can be similar to the nacelle and tower shown in  FIG. 1 . The yaw drive mechanism  100  includes a plurality of yaw powertrains  102 , for example three yaw powertrains  102 , each of which includes a drive motor  104  and associated gearing driven by the respective drive motor  104 . 
         [0042]    Each powertrain  102  drives a pinion gear  106 . The pinion gears  106  are engaged with gear teeth  108  formed on an inner periphery of a slew bearing  110 . The slew bearing  110  includes a stationary or fixed inner bearing race  112  that is fixed to a separate lock plate  114  that in turn is fixed to a separate base plate  116  is fixed to the tower of the turbine. The slew bearing  110  also includes a rotatable outer bearing race  118  that is rotatable about, and relative to, the inner bearing race  112 . 
         [0043]    With reference to  FIG. 6 , a rotatable plate  120  is fixed to the top of the outer bearing race  118 . The plate  120  is made transparent in  FIG. 5  in order to show components underneath the plate  120 . The yaw powertrains  102  are mounted on the plate  120  with the drive motors  104  on an upper side of the plate  120  and the pinion gears  106  on the opposite side of the plate  120 . In addition, the plate  120  is fixed to the nacelle. 
         [0044]    The yaw drive mechanism  100  operates as follows. One or more of the motors  104  is actuated in order to rotate the respective pinion gear  106 . Since the pinion gear(s)  106  is engaged with the teeth  108  of the inner bearing race  112  which is fixed, the plate  120  and the outer bearing race  118 , and the nacelle connected thereto, are rotated about the yaw axis A-A. 
         [0045]    With continued reference to  FIGS. 5 and 6 , once the nacelle is rotated to the correct azimuthal heading, a yaw brake mechanism  130  is used to hold or lock the nacelle at the desired azimuthal heading. In this embodiment, the yaw brake mechanism  130  uses a plurality of rotor locks  132  and a plurality of receptacles  134  that cooperate with the rotor locks  132  to achieve the locking function. The rotor locks  132  and the receptacles  134  are similar in construction and operation to the rotor locks  52  and the receptacles  54  described above whereby the piston of one of the rotor locks  132  is actuatable so as to be engaged in one of the receptacles  134  to lock the nacelle at the desired azimuthal heading. The piston of one of the rotor locks  132  is engageable with one of the receptacles  134  to achieve locking so that the single rotor lock  132  is capable of countering the full torque of the nacelle. 
         [0046]    However, in the embodiment illustrated in  FIGS. 5 and 6 , the receptacles  134  are formed in the lock plate  114  which is separate from, but fastened to, the inner bearing race  112 . In addition, the rotor locks  132  are illustrated as being arranged in a single group, sequentially arranged one after the other, instead of being separated into two groups  52   a ,  52   b  as described above for the rotor locks  52 . However, the rotor locks  132  can be separated into any number of groups, with an equal or unequal number of rotor locks in each group. 
         [0047]    As with the rotor locks  52 , there are at least two of the rotor locks  132  and at least two of the receptacles  134 . In another embodiment, the number of the receptacles  134  is greater than the number of the rotor locks  132 . The number of the rotor locks  132  and the receptacles  134  can be selected to allow the nacelle to achieve any azimuth heading around the full 360 degrees about the yaw axis A-A with less than about ±1.0 degree accuracy. For example, in one embodiment, there can be eight rotor locks  132  and twenty-five receptacles  134  to achieve this full range of azimuth headings and accuracy. 
         [0048]      FIG. 6  illustrates one of the rotor locks  132  as being actuated to the engaged condition where the piston of the rotor lock  132  is disposed within one of the receptacles  134 . The receptacles  134  are formed in an upper surface of the lock plate  114  facing the bottom surface of the plate  120 . One of the receptacles  134  can receive the piston of one of the rotor locks  132  therein when the rotor lock  132  is actuated to the engaged condition thereby preventing rotation of the nacelle about the yaw axis and the piston of the rotor lock  132  is removed from the receptacle  134  of the lock plate  114  when the rotor lock  132  is actuated to the disengaged condition thereby permitting rotation of the nacelle about the yaw axis. 
         [0049]    With reference to  FIGS. 5 and 6 , the receptacles  134  comprise generally circular indentations formed in the lock ring  114  but do not extend through the lock ring  114 . In another embodiment, the receptacles  134  can extend completely through the lock ring  114 . The receptacles  134  and the ends of the pistons of the rotor locks  132  to be disposed therein can be shaped to facilitate entry and release of the pistons of the rotor locks  132  into and from the receptacles  134 . For example, similar to the rotor locks  52  and the receptacles  54  described above, an end of each piston of the rotor locks  132  can be tapered. In addition, the interior of the receptacles  134  can have a corresponding tapered shape, for example by tapering the side walls of the receptacles or installing a tapered liner in each receptacle. 
         [0050]    Similar to the description above for the rotor locks  52  and the receptacles  54 , a selected one of the pistons of the rotor locks  132  can be actuated to an engaged condition where the end of the piston is disposed in one of the receptacles  134  to lock the azimuthal heading of the nacelle. By providing multiple rotor locks  132  and multiple receptacles  134 , the range of angles at which the nacelle can be locked is increased. For example, in the illustrated embodiment with eight rotor locks  132  and twenty-five receptacles  134 , the nacelle can achieve numerous azimuth headings around the full 360 degrees about the yaw axis A-A with less than about ±1.0 degree accuracy. In particular, the angles listed in the table above can be achieved by the nacelle using the yaw brake mechanism  130 . 
         [0051]    Returning to  FIGS. 2-4  together with  FIG. 7 , one example of a hydraulic system  150  for controlling the yaw brake mechanism  50  will now be described. A similar hydraulic system or different system can be used to control the yaw brake mechanism  130  of  FIGS. 5-6 . In this example, the hydraulic system  150  is illustrated as including solenoid control valves  152 , one for each rotor lock  52 , that can be mounted on the rotor locks  52  or at any other suitable location for controlling the flow of hydraulic fluid to and from the rotor locks  52  to control the pistons  56 . One or more pumps  154   a ,  154   b  pump hydraulic fluid from a reservoir  156  through filters  156   a ,  156   b  for supplying the pressurized hydraulic fluid, and an accumulator  158  is connected to the hydraulic fluid supply line from the pumps  154   a ,  154   b . As illustrated in  FIG. 2 , the hydraulic system  150  can be mounted on the plate  48  for rotation with the plate  48 . Electrical energy for powering the pumps  154   a ,  154   b , solenoids of the control valves  152  and other electronics can be provided via a slip ring mechanism  160 . 
         [0052]    The construction of the hydraulic system  150  illustrated in  FIGS. 2-4 and 7  is an example and many other constructions are possible. In addition, in some embodiments, the rotor locks  52  may be pneumatically or electrically actuated instead of being hydraulically actuated. 
         [0053]    The examples disclosed in this application are to be considered in all respects as illustrative and not limitative. The scope of the invention is indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.