Roller loads can be optimized and bearing life maximized with a small preload. As shown in Figure 1, its key improvement is the incorporation of preloaded TRBs that support the planet carrier and planets. Based on the knowledge gained from testing and analysis of the original design, the GRC gearbox was redesigned to improve its load-sharing characteristics and predicted fatigue. Major GRC findings include the detrimental effect of rotor moments on planetary load sharing and predicted fatigue, and the risk of bearing sliding in low-torque conditions for three-point configuration drivetrains. Two of these gearboxes, more » GB1 and GB2, were manufactured and then tested in the National Wind Technology Center's 2.5-MW dynamometer and in the field. A nonproprietary version of the gearbox containing CRBs with C3 clearances in the planetary stage was customized. To date, the GRC has focused on a 750-kW drivetrain with a three-stage, three-point-mounted gearbox. Its goals are to understand the root causes of premature gearbox failures and improve their reliability. Department of Energy established the National Renewable Energy Laboratory (NREL) Gearbox Reliability Collaborative (GRC). The cost of gearbox replacements and rebuilds and the downtime associated with these failures increase the cost of wind energy. Wind turbine gearboxes do not achieve their expected design life. Load sharing factors as high as 1.16 at extreme rotor moments and 1.08 with no moment were measured for the gearbox with cylindrical roller bearings, but the load sharing factor remained below 1.10 for the gearbox with tapered roller bearings The results show that in the wind turbine application, load sharing is not equal - even for three-planet systems with a floating central member because of the effects of gravity, rotor moments, and the resulting relative motions among the epicyclic gear components within the carrier bearing clearance. The resulting load sharing values are also compared to the mesh load factor requirements in the AGMA 6006 and IEC 61400-4 wind turbine gearbox design standards. In this paper, the reformulated model is compared to load measurements collected from two similar wind turbine gearboxes with three-planet epicyclic gear sets. More recently, this analytical model has been reformulated to include the effects of gravity, carrier bearing clearance, and external applied moments, all of which are relevant to most gearboxes and their mounting more » configuration in horizontal-axis wind turbines. Previous works have developed and validated a general closed-form analytical model of this phenomenon that describes the load sharing characteristics of epicyclic gear sets from three to six planets at any torque level. However, it is well known that certain manufacturing variations result in unequal load sharing between the parallel gear paths. In an ideal epicyclic gear set every parallel gear path transmits the same amount of torque. Planet bearings are susceptible to skidding at low input = , With bearing clearance, the bending moment can cause tooth micropitting and can induce planetbearing fatigue, leading to reduced gearbox life. Clearance in carrier bearings reduces the bearing load carrying capacity and thus the bending moment from the rotor can be transmitted into gear meshes. Bendingmoments and gravity induce fundamental excitations in the rotating carrier frame, which can increase gearbox internal loads and disturb load sharing. Influences of each of these parameters and their combined effects on the resulting planet load sharing are investigated. Planet load sharing is a combined effect of gravity, bending moment, bearing clearance, and input torque. This drivetrain model is validated against the experimental data of Gearbox Reliability Collaborative for gearbox internal loads. A flexible main shaft, planetary carrier, housing, and gear shafts are modeled using reduced degrees-of-freedomthrough modal compensation. A three dimensional multibody dynamic model is established, including gravity, bending moments, fluctuating mesh stiffness, nonlinear tooth contact, and bearing clearance. This computational work investigates planetary gear load sharing of three-mount suspension wind turbine gearboxes.

Freedom planet torque levels