There is a known and ever-growing tendency in wind turbine technology towards increasing the size of its machinery. Consequently, this tendency is paired up with attempts to reduce the elevated weight of the components involved, since less weight is equivalent to less stress and load on the structure, which further translates to a reduction in operational costs.
In the latest versions in wind turbine design, ongoing efforts are being made to integrate all the components constituting a wind turbine into one compact design so that the rotor hub is directly connected to the gearbox's input shaft and gearbox bearings support the rotor hub, or, contrariwise, the rotor hub bearings support the gearbox entrance shaft.
Assembly of the wind turbine transmission comprises the rotor hub, the wind turbine nacelle as supporting means and the planetary type gearbox having at least one sun wheel, around which rotate one or more planets engaging in a ring wheel, supported by a planetary carrier rotating in relation to the central sun wheel.
A problem nevertheless arises with this type of design in that the forces and deformations of the rotor hub directly affect the gearbox, since the rotor hub and the gearbox input shaft, in this type of design, call for a rigid connection. These deformations imposed on the gearbox necessarily imply planetary gearbox stage misalignments, which are almost always the causes behind internal faults in gearboxes.
One known solution to solve these deformation problems is the use of a bogie plate on the gearbox's planetary carrier. The bogie plate comprises several housings equipped with planet shafts, so that on both sides of the bogie plate, in each planet shaft, planets can be mounted, installed together with the pertinent bearings. These planetary carrier equipped with a bogie plate absorb certain misalignments, keeping them from affecting the gears in the gearbox.
There are known solutions incorporating a bogie plate coupled to the planetary carrier with fastening elements, however, these solutions, on the one hand, call for complex assembly operations that imply spending a substantial length of time and require highly strengthened materials, thus making them expensive, and, on the other hand, require continuous maintenance and monitoring, since the joint behavior cannot be determined with certainty in the long term.
Other solutions are known to integrate, as a single piece, the bogie plate together with the planetary carrier, as shown in patent EP2072863 filled by the same applicant, which solves the inconveniences of the bolted joints between the bogie plate and the planetary carrier.
Notwithstanding the above, both in the solution of the bogie plate fastened to the planetary carrier as well as the solution of the bogie plate and planetary carrier in a single piece, when there is little torque in the gearbox due to the reduced friction between the shaft on which the planets are mounted (hereinafter known as the planetary shaft) and the bogie plate housing, and likewise due to reduced friction in the planetary bearings, a rotating planet produces a planetary shaft rotation relative to the bogie plate housing.
This translates into a grinding of the housing walls, consequently filling the gears with shavings and increasing the tension between teeth from the entrapment of these shavings, which, as a result, causes a gearbox fault.
This problem is further intensified when the planetary bearings are pre-loaded, since its resistance to rotation would be higher and require an elevated level of load to overcome this effect.
Given that there are moments of little torque, i.e., having reduced load, often during the life of a wind turbine, for instance, when there is no wind, when disconnected from the grid, during start-up or when gathering speed, a solution to this problematic situation is necessary.