Patent Publication Number: US-10330174-B2

Title: Gear assembly for a wind turbine gearbox having a flexible pin shaft and carrier

Description:
FIELD 
     The present disclosure relates in general to wind turbines, and more particularly to a gear assembly for a wind turbine gearbox having a flexible pin shaft and carrier made, at least in part, via additive manufacturing. 
     BACKGROUND 
     Generally, a wind turbine includes a tower, a nacelle mounted on the tower, and a rotor coupled to the nacelle. The rotor generally includes a rotatable hub and a plurality of rotor blades coupled to and extending outwardly from the hub. Each rotor blade may be spaced about the hub so as to facilitate rotating the rotor to enable kinetic energy to be converted into usable mechanical energy, which may then be transmitted to an electric generator disposed within the nacelle for the production of electrical energy. Typically, a gearbox is used to drive the electric generator in response to rotation of the rotor. For instance, the gearbox may be configured to convert a low speed, high torque input provided by the rotor to a high speed, low torque output that may drive the electric generator. 
     The gearbox generally includes a gearbox housing containing a plurality of gears (e.g., planetary, ring and/or sun gears as well as non-planetary gears) connected via one or more planetary carriers and bearings for converting the low speed, high torque input of the rotor shaft to a high speed, low torque output for the generator. In addition, each of the gears rotates about a pin shaft arranged within the one or more planetary carriers. Lubrication systems are often used within the gearbox to circulate oil therethrough, thereby decreasing the friction between the components of the gearbox as well as providing cooling for such components. In addition, the oil is configured to provide corrosion protection while also flushing debris from the lubricated surfaces. 
     Deformation of many of the gearbox components results in a non-ideal load distribution between the gears. Though all loaded components deform under load, deformation of interfaces between the components is more difficult to predict. The pin shafts of the gearbox therefore often require extensive machining. More particularly, the pin-end connections of the pin shafts, which are loaded in bending, can be problematic by design. Thus, such gearbox components can experience an uneven load distribution. 
     Accordingly, an improved gearbox assembly for a wind turbine that addresses the aforementioned issues would be welcomed in the art. 
     BRIEF DESCRIPTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In one aspect, the present disclosure is directed to a method for manufacturing a gear assembly of a gearbox of a wind turbine. The method includes forming a carrier of the gear assembly and at least one pin shaft of the gear assembly as a single part. Further, the pin shaft(s) has a variable cross-section. The method also includes forming one or more voids in the gear assembly via an additive manufacturing process. As such, the void(s) are configured to increase flexibility of the pin shaft(s) so as to improve a load distribution of the carrier. 
     In one embodiment, the additive manufacturing process may include binder jetting, material jetting, laser cladding, cold spray deposition, directed energy deposition, powder bed fusion, material extrusion, vat photopolymerisation, or any other suitable additive manufacturing process. 
     In another embodiment, the method may include forming at least one additional feature into the pin shaft(s) via additive manufacturing. More specifically, in certain embodiments, the additional feature(s) may include an oil path, one or more ribs or structural supports on and interior surface of one or more of the voids, a cooling channel, an inspection path, a void removal feature, a signal wiring path, a sensor recess, or a locating feature, or any other features that can be easily printed or formed therein. 
     In further embodiments, the method may include forming the carrier and the pin shaft(s) as the single part via additive manufacturing. 
     In alternative embodiments, the step of forming the carrier and the pin shaft(s) may include casting the carrier and the pin shaft(s) as a single part. In such embodiments, the step of casting the carrier and the pin shaft(s) may include pouring a liquid material into a mold of the carrier and the pin shaft(s) and allowing the liquid material to solidify in the mold so as to form the carrier and the pin shaft(s) as the single part. Alternatively, the step of casting the carrier and the pin shaft(s) may include pouring a liquid material into a mold of the carrier, allowing the liquid material to solidify in the mold so as to form the carrier, and then additively molding or printing the pin shaft(s) to the cast carrier to form the integral part. 
     In additional embodiments, the method may include splitting the carrier into a main portion and a secondary portion after forming the carrier and the at least one pin shaft as the single part, the main portion comprising the at least one pin shaft so as to assist with assembly of the gears onto the pin shaft(s). As such, after splitting, the method may include removing the secondary portion of the carrier from the main portion and assembling a gear onto the pin shaft(s) of the main portion. The method then includes replacing the secondary portion onto the main portion. 
     In several embodiments, the method may include determining a location for the one or more voids based on a load path of the carrier. For example, in one embodiment, the method may include forming the one or more voids in the pin shaft(s) in a lengthwise center location thereof so as to load the gears as evenly as possible. 
     In particular embodiments, the method may also include depositing, e.g. printing, bearing material onto an exterior surface of the pin shaft(s). 
     In another aspect, the present disclosure is directed to a method for manufacturing a gear assembly of a gearbox of a wind turbine. The method includes forming a carrier of the gear assembly. The method also includes forming at least one pin shaft of the gear assembly having a variable cross-section. Further, the method includes forming one or more voids in the gear assembly via an additive manufacturing process. Moreover, the void(s) are configured to increase flexibility of the pin shaft(s) so as to improve a load distribution of the carrier. In addition, the method includes securing the pin shaft(s) to the carrier. 
     It should also be understood that the method may further include any of the additional features and/or steps described herein. 
     In addition, the step of forming the carrier and forming the pin shaft(s) may include casting the carrier and casting the pin shaft(s) as separate parts. Thus, in certain embodiments, the method may include securing the pin shaft(s) to the carrier via one or more fasteners. 
     In further embodiments, the method may include depositing bearing material onto an exterior surface of the pin shaft(s) and covering the one or more fasteners with the deposited bearing material. 
     In yet another aspect, the present disclosure is directed to a gearbox assembly. The gearbox assembly includes a gearbox housing and a planetary gear system configured therein. The planetary gear system includes a plurality of planet gears, at least one sun gear, at least one ring gear, at least one carrier operatively coupled with the plurality of planet gears, and a plurality of pin shafts. Each of the planet gears is arranged so as to rotate around one of the plurality of pin shafts. Further, each of the planet gears is engaged with the ring gear and configured to rotate about the sun gear. Further, the pin shaft(s) is integral with the carrier. Moreover, the pin shaft(s) includes a variable cross-section containing one or more voids formed therein. As such, the variable cross-section of the pin shaft(s) is configured to increase flexibility of the pin shaft(s) so as to improve a load distribution of the carrier. 
     It should also be understood that the gearbox assembly may further include any of the additional features described herein. 
     In addition, the gearbox assembly may include at least one seal arranged on an exterior surface of the pin shaft(s) so as to seal the one or more voids, which may prevent swarf from entering the void(s) while machining. In addition, the seal(s) may also be arranged to guide the oil supply or the oil draining. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  illustrates a perspective view of one embodiment of a wind turbine according to conventional construction; 
         FIG. 2  illustrates a detailed, internal view of one embodiment of a nacelle of a wind turbine according to conventional construction; 
         FIG. 3  illustrates a cross-sectional view of one embodiment of a gearbox assembly of a wind turbine according to conventional construction; 
         FIG. 4  illustrates a cross-sectional view of one embodiment of a gearbox assembly of a wind turbine according to the present disclosure; 
         FIG. 5  illustrates a detailed, cross-sectional view of one embodiment of an integral planetary carrier and flexible pin shaft of the gearbox assembly assembled with the planet gear according to the present disclosure; 
         FIG. 6  illustrates a detailed, cross-sectional view of one embodiment of an integral planetary carrier and flexible pin shaft of the gearbox assembly disassembled from the planet gear according to the present disclosure; 
         FIG. 7  illustrates a detailed, cross-sectional view of one embodiment of a planetary carrier and a separate flexible pin shaft of the gearbox assembly according to the present disclosure, particularly illustrating the pin shaft mounted to the planetary carrier; 
         FIG. 8  illustrates a detailed, cross-sectional view of one embodiment of a planetary carrier and a separate flexible pin shaft of the gearbox assembly according to the present disclosure, particularly illustrating the pin shaft dismounted from the planetary carrier; and, 
         FIG. 9  illustrates a detailed, cross-sectional view of one embodiment of a separate flexible pin shaft of the gearbox assembly according to the present disclosure, particularly illustrating an oil path formed therein; 
         FIG. 10  illustrates a front view of one embodiment of an integral planetary carrier and a plurality of flexible pin shafts of the gearbox assembly according to the present disclosure; 
         FIG. 11  illustrates a detailed, cross-sectional view of one embodiment of a separate flexible pin shaft of the gearbox assembly according to the present disclosure, particularly illustrating a non-conical void formed therein; 
         FIG. 12  illustrates detailed, front views of a plurality of flexible pin shafts of the gearbox assembly according to the present disclosure, particularly illustrating different shapes of voids formed in the pin shafts; 
         FIG. 13  illustrates a detailed, cross-sectional view of one embodiment of a separate flexible pin shaft of the gearbox assembly according to the present disclosure, particularly illustrating various additional features formed therein; 
         FIG. 14  illustrates a detailed, cross-sectional view of one embodiment of a separate flexible pin shaft of the gearbox assembly according to the present disclosure, particularly illustrating a sensor wire path and sensor recess formed therein; 
         FIG. 15  illustrates a perspective view of one embodiment of a planetary carrier and a plurality of integral pin shafts of a gearbox assembly according to the present disclosure; 
         FIG. 16  illustrates a side view of the planetary carrier and the plurality of integral pin shafts of the gearbox assembly of  FIG. 15 ; 
         FIG. 17  illustrates a cross-sectional view of the planetary carrier and the plurality of integral pin shafts of the gearbox assembly of  FIG. 16 ; 
         FIG. 18  illustrates a detailed, cross-sectional view of another embodiment of a flexible pin shaft of the gearbox assembly according to the present disclosure, particularly illustrating various additional features formed therein; and 
         FIG. 19  illustrates a flow diagram of one embodiment of a method for manufacturing a gear assembly of a gearbox of a wind turbine according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Generally, the present disclosure is directed to a gear assembly having at least one flexible pin shaft and/or carrier and methods and manufacturing same. It should be understood that the pin shafts described herein are meant to encompass any pin shafts within the gearbox, including pin shafts at planetary stages as well as non-planetary stages (e.g. helical stages). In one embodiment, the carrier and pin shaft(s) may be formed as an integral or single part. Alternatively, the carrier and pin shaft(s) may be formed as separate components. In addition, the carrier and pin shaft(s) may be formed via casting, additive manufacturing, or combinations thereof. More specifically, the flexible pin shaft(s) has a variable cross-section that includes one or more voids formed via additive manufacturing. Further, the void(s) may also be formed into the carrier, e.g. adjacent to the pin shaft(s). As such, the void(s) are configured to increase flexibility thereof so as to improve a load distribution of the carrier. 
     Thus, the present disclosure provides many advantages not present in the prior art. For example, the integral carrier/flexible pin shaft avoids interfaces between parts, thereby avoiding machining cost and/or bolting of the interfaces, handling of the extra parts, as well as the failure modes of the interfaces or variance in the behavior of the interface due to manufacturing tolerances allowed. Alternatively, the present disclosure may keep the carrier separate from flexible pin shaft, in which case the pin shaft can be formed via additive manufacturing and the carrier may be formed via a more simplistic manufacturing process, such as casting, to take advantage of the different advantages of both techniques. In either case, the flexible pin shaft(s) provide a more even load distribution than pin shafts having a constant or uniform cross-section. 
     Referring now to the drawings,  FIG. 1  illustrates a perspective view of one embodiment of a wind turbine  10  of conventional construction. As shown, the wind turbine  10  includes a tower  12  extending from a support surface  14 , a nacelle  16  mounted on the tower  12 , and a rotor  18  coupled to the nacelle  16 . The rotor  18  includes a rotatable hub  20  and at least one rotor blade  22  coupled to and extending outwardly from the hub  20 . For example, in the illustrated embodiment, the rotor  18  includes three rotor blades  22 . However, in an alternative embodiment, the rotor  18  may include more or less than three rotor blades  22 . Each rotor blade  22  may be spaced about the hub  20  to facilitate rotating the rotor  18  to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub  20  may be rotatably coupled to an electric generator  24  ( FIG. 2 ) positioned within the nacelle  16  to permit electrical energy to be produced. 
     As shown, the wind turbine  10  may also include a turbine control system or a turbine controller  26  centralized within the nacelle  16 . For example, as shown in  FIG. 2 , the turbine controller  26  is disposed within a control cabinet mounted to a portion of the nacelle  16 . However, it should be appreciated that the turbine controller  26  may be disposed at any location on or in the wind turbine  10 , at any location on the support surface  14  or generally at any other location. In general, the turbine controller  26  may be configured to transmit and execute wind turbine control signals and/or commands in order to control the various operating modes (e.g., start-up or shut-down sequences) and/or components of the wind turbine  10 . 
     Referring now to  FIG. 2 , a simplified, internal view of a nacelle  16  of the wind turbine  10  according to conventional construction is illustrated. As shown, the generator  24  may be disposed within the nacelle  16 . In general, the generator  24  may be coupled to the rotor  18  of the wind turbine  10  for producing electrical power from the rotational energy generated by the rotor  18 . For example, as shown in the illustrated embodiment, the rotor  18  may include a rotor shaft  32  coupled to the hub  20  for rotation therewith. The rotor shaft  32  may, in turn, be rotatably coupled to a generator shaft  34  of the generator  24  through a gearbox assembly  36 . As is generally understood, the rotor shaft  32  may provide a low speed, high torque input to the gearbox assembly  36  in response to rotation of the rotor blades  22  and the hub  20 . The gearbox assembly  36  may then be configured to convert the low speed, high torque input to a high speed, low torque output to drive the generator shaft  34  and, thus, the generator  24 . In alternative embodiments, the rotor shaft  32  may be eliminated and the rotatable hub  20  may be configured to turn the gears of the gearbox assembly  36 , rather than requiring a separate rotor shaft  32 . 
     Referring now to  FIG. 3 , a cross-sectional view of a gearbox assembly  36  according to conventional construction is illustrated. As shown, the gearbox assembly  36  includes planetary gear system  38  housed within a gearbox housing  37 . More specifically, the gear system  38  includes a plurality of gears (e.g., planetary, ring, sun, helical, and/or spur gears) and bearings  39  for converting the low speed, high torque input of the rotor shaft  32  to a high speed, low torque output for the generator  24 . For example, as shown, the input shaft  32  may provide an input load to the gear system  38  and the system  38  may provide an output load to the generator  24  ( FIG. 2 ) as is generally known in the art. Thus, during operation, input load at an input rotational speed is transmitted through the planetary gear system  38  and provided as output load at output rotational speed to the generator  24 . 
     Further, the planetary gear system  38  includes a first planetary carrier  40  and a second planetary carrier  42  operatively coupling a plurality of gears. Further, as shown, the planetary gear system  38  includes, at least, a ring gear  41 , one or more planet gears  44 , a sun gear  46 , one or more first pin shafts  43 , and one or more second pin shafts  45 . For example, in several embodiments, the gear system  38  may include one, two, three, four, five, six, seven, eight, or more planet gears  44 . Further, each of the gears  41 ,  44 ,  46  includes a plurality of teeth. The teeth are sized and shaped to mesh together such that the various gears  41 ,  44 ,  46  engage each other. For example, the ring gear  41  and the sun gear  46  may each engage the planet gears  44 . In addition, it should be understood that the gears  41 ,  44 ,  46  described herein may include any suitable type of gears, including but not limited to spur gears, face gears, helical gears, double helical gears, or similar. 
     In some embodiments, one or both of the planetary carriers  40 ,  42  may be stationary. In these embodiments, the input shaft  32  may be coupled to the ring gear  41 , and input loads on the input shaft  32  may be transmitted through the ring gear  41  to the planet gears  44 . Thus, the ring gear  41  may drive the gear system  38 . In other embodiments, the ring gear  41  may be stationary. In these embodiments, the input shaft  32  may be coupled to the planetary carriers  40 ,  42 , and input loads on the input shaft  32  may be transmitted through the planetary carriers  40 ,  42  to the planet gears  44 . Thus, the planetary carriers  40 ,  42  may drive the gear system  38 . In still further embodiments, any other suitable component, such as the planet gear  44  or the sun gear  46 , may drive the gear system  38 . 
     Still referring to  FIG. 3 , the sun gear  46  defines a central axis  49 , and thus rotates about this central axis  49 . The ring gear  41  may at least partially surround the sun gear  46 , and be positioned along the central axis  49 . Further, the ring gear  41  may (if rotatable) thus rotate about the central axis  49 . Each of the planet gears  44  may be disposed between the sun gear  46  and the ring gear  41 , and may engage both the sun gear  46  and the ring gear  41 . For example, the teeth of the gears may mesh together, as discussed above. Further, each of the planet gears  44  may define a central planet axis  48 , as shown. Thus, each planet gear  44  may rotate about its central planet axis  48 . Additionally, the planet gears  44  and central planet axes  48  thereof may rotate about the central axis  49 . 
     The gearbox assembly  36  may also include a lubrication system or other means for circulating oil throughout the gearbox components. For example, as shown in  FIG. 3 , the gearbox assembly  36  may include a plurality of oil passages  47  that are configured to transfer oil therethrough. As is generally understood, the oil may be used to reduce friction between the moving components of the gearbox assembly  36  and may also be utilized to provide cooling for such components, thereby decreasing component wear and other losses within the gearbox assembly  36  and increasing the lifespan thereof. In addition, the oil may contain properties that prevent corrosion of the internal gearbox components. 
     Referring now to  FIG. 4 , a cross-sectional view of a gearbox assembly  136  according to the present disclosure is illustrated. As shown, the gearbox assembly  136  includes planetary gear system  138  housed within a gearbox housing  137 . More specifically, the gear system  138  includes a plurality of gears (e.g., planetary, ring and/or sun gears) and bearings  139  for converting the low speed, high torque input of the rotor shaft  132  to a high speed, low torque output for the generator (not shown). For example, as shown, the input shaft  132  may provide an input load to the gear system  138  and the system  138  may provide an output load to the generator via output shaft  134 . Thus, during operation, input load at an input rotational speed is transmitted through the planetary gear system  138  and provided as output load at output rotational speed to the generator. 
     Further, as shown, the planetary gear system  138  includes a first planetary carrier  140  and a second planetary carrier  142  operatively coupling a plurality of gears. It should also be understood that the planetary gear system  138  may have any suitable arrangement of planetary stages and/or helical stages. In the depicted embodiment, which is provided for illustrated purposes only, the planetary gear system  138  includes, at least, a ring gear  141 , one or more planet gears  144 , a sun gear  146 , one or more first pin shafts  143 , and one or more second pin shafts  145 . For example, in several embodiments, the gear system  138  may include one, two, three, four, five, six, seven, eight, or more planet gears  144 . Further, each of the gears  141 ,  144 ,  146  includes a plurality of teeth. The teeth are sized and shaped to mesh together such that the various gears  141 ,  144 ,  146  engage each other. For example, the ring gear  141  and the sun gear  146  may each engage the planet gears  144 . In addition, as mentioned, it should be understood that the gears  141 ,  144 ,  146  described herein may include any suitable type of gears, including but not limited to spur gears, face gears, helical gears, double helical gears, or similar. 
     In some embodiments, the planetary carriers  140 ,  142  may be stationary. In these embodiments, the input shaft  132  may be coupled to the ring gear  141 , and input loads on the input shaft  132  may be transmitted through the ring gear  141  to the planet gears  144 . Thus, the ring gear  141  may drive the gear system  138 . In other embodiments, the ring gear  141  may be stationary. In these embodiments, the input shaft  132  may be coupled to the planetary carriers  140 ,  142 , and input loads on the input shaft  132  may be transmitted through the planetary carriers  140 ,  142  to the planet gears  144 . 
     Still referring to  FIG. 4 , the sun gear  146  defines a central axis  149 , and thus rotates about this central axis  149 . The ring gear  141  may at least partially surround the sun gear  146 , and be positioned along the central axis  149 . For example, the ring gear  141  may be aligned with the sun gear  146  along the central axis  149 , or may be offset from the sun gear  146  along the axis  149 . The ring gear  141  may (if rotatable) thus rotate about the central axis  149 . Each of the planet gears  144  may be disposed between the sun gear  146  and the ring gear  141 , and may engage both the sun gear  146  and the ring gear  141 . In addition, as shown generally in  FIGS. 4-18 , the pin shaft(s)  143 ,  145  and/or the planetary carrier(s)  140 ,  142  of the present disclosure may include one or more voids  152  formed therein so as to increase flexibility thereof, which improves the load distribution of the planetary carrier  140 ,  142 . Thus, as shown, the pin shaft(s)  143 ,  145  may include a variable cross-section as opposed to a constant cross-section of prior art pin shafts. 
     Referring now to  FIGS. 4-6 , the pin shaft(s)  143 ,  145  of the present disclosure may be formed integrally with the planetary carrier  140 ,  142 , respectively, (i.e. in contrast to conventional gearboxes as shown in  FIG. 3  where the pin shaft(s)  43 ,  45  are separate from the planetary carrier(s)  40 ,  42 ). In other words, in one embodiment, the pin shaft(s)  143 ,  145  and the planetary carrier  140 ,  142  may be a formed as a single part. For example, in one embodiment, the pin shaft(s)  143 ,  145  may be formed integrally with the planetary carrier  140 ,  142  via an additive manufacturing process. As used herein, additive manufacturing generally refers to processes used to create a three-dimensional object in which layers of material are formed under computer control to create an object. More specifically, the additive manufacturing processes described herein may include binder jetting, material jetting, laser cladding, cold spray deposition, directed energy deposition, powder bed fusion, material extrusion, vat photopolymerisation, or any other suitable additive manufacturing process. In one exemplary embodiment, the pin shaft(s)  143 ,  145  may be formed integrally with the planetary carrier  140  via sand binder jetting that utilizes ductile iron or carbon steel. 
     In alternative embodiments, the pin shaft(s)  143 ,  145  may be formed integrally with the planetary carrier  140 ,  142  via casting the pin shaft(s)  143 ,  145  and the planetary carrier(s)  140 ,  142  (e.g. the first stage planetary carrier  140  with a plurality of first stage pin shafts  142 ) into a single mold. In such embodiments, casting of the planetary carrier  140 ,  142  and the pin shaft(s)  143 ,  145  may include pouring a liquid material into a mold of the planetary carrier  140 ,  142  and the pin shaft(s)  143 ,  145  and allowing the liquid material to solidify in the mold so as to form the planetary carrier  140 ,  142  and the pin shaft(s)  143 ,  145  as the single part. Alternatively, the planetary carrier  140 ,  142  and the pin shaft(s)  143 ,  145  may be formed by pouring a liquid material into a mold of the planetary carrier  140 ,  142 , allowing the liquid material to solidify in the mold so as to form the planetary carrier  140 ,  142 , and then additively molding or printing the pin shaft(s)  143 ,  145  to the cast carrier  140 ,  142  to form the integral part. 
     In addition, as shown in  FIGS. 15 and 16 , the planetary carrier(s)  140 ,  142  may be split into a main portion  151  and a secondary portion  153  along split line  147  after it is formed to assist with assembly of the gears onto the pin shaft(s)  143 ,  145 . Further, as shown, the main portion  151  of the planetary carrier(s)  140 ,  142  may include the pin shaft(s)  143 ,  145 . As such, after splitting, the secondary portion  153  of the planetary carrier(s)  140 ,  142  from the main portion  151  such that the gears (not shown) can be assembled onto the pin shafts. The secondary portion  153  can then be secured to the main portion  151 , e.g. via one or more fasteners. 
     Once the integral pin shaft(s)  143 ,  145  and planetary carrier(s)  140 ,  142  is formed (or just the pin shaft(s)  143 ,  145 ), further additive manufacturing techniques may be used to create the variable cross-section into the pin shaft(s)  143 ,  145 . For example, as shown in  FIGS. 4-9 , an additive manufacturing process (e.g. such as sand binder jetting or lost wax casting methods) may be used to create the void(s)  152  into the pin shaft(s)  143  and/or the carrier(s)  140 ,  142 . As such, the variable cross-section of the pin shaft(s)  143 ,  145  is configured to increase flexibility of the pin shaft(s)  143 ,  145  so as to improve a load distribution of the planetary carrier  140 ,  142 . More specifically, as shown in  FIGS. 4-10 , the void(s)  152  may have a round, conical shape that tapers from a first end  154  to a second end  156  of the pin shaft(s)  143 . Further, as shown particularly in  FIG. 10 , the flexible pin shafts  143 ,  145  allow for the possibility to provide directional deformation (as represented by the arrows) that helps to improve the load distribution on the gears  144  and/or on the bearings (not shown). As used herein, the term “variable cross-section” generally refers to any suitably shaped cross-section that is non-uniform and/or non-constant over the length of the pin shaft(s)  143 . 
     In alternative embodiments, as shown in  FIG. 11 , the void(s)  152  may have a non-conical shape. For example, as shown, the void(s)  152  may be thicker at the first and second ends  154 ,  156  and thinner in the middle. In addition, as shown in  FIG. 12 , it should be further understood that the void(s)  152  may have any suitable shape that may be adjusted to match the desired local stiffness. For example, as shown,  FIG. 12  illustrates three different cross-sections of a single representative pin shaft  143  along the longitudinal axis of the pin shaft  143 . Thus, as shown, the cross-section of the pin shaft  143  (and more specifically the void  152 ) can be varied (e.g. rotated) axially to facilitate low stresses along the load path. Accordingly, as shown, the cross-section of the void  152  of the pin shaft  143  may have a different shape along the axis to match the desired corresponding stiffness. 
     In additional embodiments, the location(s) for the void(s)  152  may be determined based on a load path of the planetary carrier(s)  140 ,  142 . For example, in one embodiment, the void(s)  152  may be formed in the pin shaft(s)  143 ,  145  in a lengthwise center location thereof so as to move the load path closer to the center of the pin shaft(s)  143 ,  145 . More specifically, as shown in  FIGS. 4-14 , the voids(s)  152  taper towards the lengthwise center of the pin shaft(s)  143 ,  145  to maintain the stresses in the pin shaft(s)  143 ,  145  and the planetary carrier(s)  140 ,  142  within acceptable limits while yielding deformation that creates a desired load pattern in the gears. 
     Referring particularly to  FIGS. 13 and 14 , at least one additional feature  160  may also be formed or printed into the pin shaft(s)  143  via additive manufacturing. More specifically, in certain embodiments, the additional feature  160  may include an oil path (e.g. an oil supply path, an oil drain (removal) path, an oil distribution manifold, an oil collection channel, an oil buffer, and/or similar), one or more ribs or structural supports on and interior surface of one or more of the voids, a cooling channel, an inspection path, a void removal feature, a signal wiring path, one or more recesses, or a locating feature, or any other features that can be easily printed or formed therein. 
     For example, as shown in  FIGS. 9 and 17-18 , one or more oil paths  158  may also be formed through the pin shaft(s)  143 . More specifically, as shown particularly in  FIG. 9 , an oil path  158  may be formed from an exterior surface  155  of the pin shaft(s)  143  at the first end  154  thereof and through one of the voids  152  to the second end  156  of the pin shaft(s)  143 . In another embodiment, as shown in  FIG. 17 , the oil path  158  may be completely separate from the voids  152 . In further embodiments, any number of oil paths may be formed into the pin shaft(s)  143 ,  145  via any suitable additive manufacturing process. 
     In additional embodiments, as shown in  FIG. 13 , the additional feature(s)  160  may also include a cooling channel  162 . Further, as shown in  FIGS. 17 and 18 , the additional feature(s)  160  may include one or more ribs  165  or structural supports on and interior surface of one or more of the voids  152 . Such ribs  165  are configured to locally increase stiffness where desired. 
     In addition, as shown in  FIG. 14 , the additional feature(s)  160  may include a signal wiring path  164  and/or a sensor recess  166  configured to receive a sensor or probe. Thus, as shown, a sensor wire and associated sensor can be positioned in the pin shaft(s)  143 . Further, as shown in  FIG. 18 , the additional feature(s)  160  may include an inspection path or probe recess configured to receive a proximity sensor (e.g. an inductive, infrared or ultrasonic sensor) that can take measurements of the curves at the end of the void(s)  152  opposite the planetary carrier(s)  140 ,  142  as well as measuring pin deflection. 
     In further embodiments, the additional feature(s)  160  may include a locating feature  168 . For example, as shown in  FIGS. 5-6 and 13-14 , the locating features  168  may be flanges that assist in aligning the pin shaft(s)  143 ,  145  with the planetary carrier(s)  140 ,  142 . It should be understood that the additional feature(s)  160  may further include any other features that can be easily printed or formed therein. 
     In yet another embodiment, the additional feature(s)  160  may include void removal feature  169 . For example, as shown in  FIG. 18 , one or more of the voids  152  may be created to facilitate removal of sand binder jet cores used to cast the internal pin geometry. Such voids  152  are referred to herein as void removal features  169 . In addition, the pin shaft  142  may include additional number of additional recesses, such as recess  174 , configured to receive at least a portion of a bearing, such as a journal or roller bearing frame. Further, as shown, the recess(es)  174  may be designed to receive a retaining ring of a bearing. 
     Referring particularly to  FIG. 13 , the gearbox assembly  136  may further include at least one seal  170  arranged on the exterior surface  155  of the pin shaft(s)  143  so as to seal the one or more voids  152 . In such embodiments, the seal(s)  170  are configured to allow the voids  152  to be multi-functional, e.g. to create a lubricant supply or drain, to facilitate cleaning, and/or to prevent dirt out once cleaned, e.g. during machining or during operation. 
     Referring now to  FIG. 19 , a flow diagram of one embodiment of a method  100  for manufacturing the planetary carrier  140  and the pin shaft(s)  143  of the gearbox assembly  136  of the wind turbine  10  is illustrated. As shown at  102 , the method  100  includes forming the planetary carrier(s)  140 ,  142 . As shown at  104 , the method  100  includes forming the pin shaft(s)  143 ,  145 . For example, as shown in  FIGS. 7 and 8 , the planetary carrier(s)  140 ,  142 , and/or the pin shaft(s)  143 ,  145  may be formed via casting the components as separate parts. It should be understood that any suitable casting technique may be used, including but not limited to, centrifugal casting, core plug casting, die casting, glass casting, investment casting, lost-foam casting, lost-wax casting, molding, permanent mold casting, rapid casting, sand casting, and/or slip-casting, etc. 
     As shown at  106 , the method  100  includes forming one or more voids  152  in the pin shaft(s)  143 ,  145  to create a variable cross-section of the pin shaft(s)  143 ,  145  via additive manufacturing. As such, the variable cross-section of the pin shaft(s)  143 ,  145  is configured to increase flexibility of the pin shaft(s)  143 ,  145  so as to improve a load distribution of the planetary carrier  140 ,  142 . 
     As shown at  108 , the method  100  includes securing the pin shaft(s)  143 ,  145  to the planetary carrier(s)  140 ,  142 , respectively. More specifically, as shown in  FIGS. 7, 9, 11, and 13-14 , the method  100  may include securing the pin shaft(s)  143 ,  145  to the planetary carrier(s)  140 ,  142  via one or more fasteners  174 . 
     In further embodiments, as shown  FIGS. 13 and 14 , the pin shaft(s)  143  may further include bearing material  172  disposed onto the exterior surface  155  thereof. For example, in one embodiment, the method  100  may include printing the bearing material  172  onto the exterior surface  155  of the pin shaft(s) 143 layer by layer, e.g. so as to build up a journal bearing thereon. As such, the method  100  creates an adhesion or metallurgical bond between the pin shaft(s)  143  and the bearing material  172 . Thus, the bond replaces conventional fasteners of prior art systems and eliminates interference stresses, thereby enabling a smaller space envelope. In addition, the method  100  requires less material/weight and reduces machining and assembly time for the journal bearing. 
     More specifically, in certain embodiments, the bearing material  172  may include various metals or metal alloys, including, for example, a copper alloy (e.g. bronze). Thus, the bearing material  172  may be applied to the exterior surface  155  of the pin shaft(s)  143  to provide improved wear characteristics under loading (especially at startup and shutdown, when an oil film may be insufficient to separate the rotating and non-rotating surfaces). In addition, as shown, the method  100  may further include completely or partially covering the exterior surface  155 , thereby optionally covering the one or more fasteners  174  with the deposited bearing material  172 . Accordingly, by printing the bearing material  172 , said material can be thinner than conventional bearings (e.g. about 2 millimeters (mm) as opposed to 15 mm). 
     In certain embodiments, the bearing material  172  may be printed via a programmed robotic system capable of printing the bearing material  172  that enables additional productivity benefits and repeatability relative to a manual process. Traditionally, to harden the surface of the bearing, the entire journal would need to be heat treated. Hardening of the bearing is only needed on the surface and can be accomplished with concentrated/amplified light energy. As such, the method  100  of the present disclosure improves speed and automation of the process and provides optimal material properties only where desired. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.