Gear box, seal and cover arrangements

A gearbox (18) for a wind turbine has a bearing arrangement (34) positioned on the downwind side of a first stage planet carrier (26) at a single locus. The planet carrier (26) has a portion (27) extending radially inwards and axially downwind from the planet gears. This reduces the diameter, weight and cost of the bearing arrangement. The diameter, for example, can be less than the outer diameter of the input shaft. In addition, bearings positioned on the upwind side of the first stage planet carrier (26) are not required. Thus, the weight of the gearbox (18) is supported between the two theoretical support points of the pair of back to back tapered roller bearings (34) at the down wind side of the first stage planet carrier (26). The support for the gearbox is more stable compared to the traditional arrangement with face to face bearings in which the weight of the gearbox lies on the extended line of the two theoretical support points. The absence of upwind bearings for the first stage planet carrier (26) means that the front cover (1108) is not subject to external forces. Therefore a horizontal-split thin cover can be used on the upwind side of the first stage ring gear (28). This arrangement can reduce the weight of the housing by about one ton compared to the traditional housing for the upwind bearings. A member of unitary construction comprising gearbox flange (1240), input shaft (24) and first stage planet carrier (26), which can be cast as one piece, reduces the weight of this part compared to previous designs having separate components. In addition the machining required of the connector and coupling is reduced, and difficulties aligning individual components are eliminated. The dimension of the output side of the first stage planet carrier (26) is increased so that the stress level on this component is reduced. Therefore low cost cast iron can be used.