Patent Application
20140150449
The present disclosure relates to gas turbine engines and more particularly to improvements in the cooling of coupled shafts.
Shaft and bearing deformation may occur at the interface of a bearing inner race and the shaft to which it is coupled, because of the heat generated by the turbine rotor and conducted by the shaft supporting the turbine rotor, especially when the bearing is close to the turbine rotor. This phenomenon of coning has been found to be especially problematic in gas turbine engines where the main shaft bearing is between the compressor module and the turbine module and in close proximity to the turbine module. The thermal conduction from the turbine rotor has resulted in coning of the shaft as well as of the bearing, leading to premature bearing distress.
In one aspect, there is provided a gas turbine engine having at least a spool assembly including at least a compressor rotor and a turbine rotor connected by a shaft assembly, the shaft assembly comprising: a compressor shaft portion connected to the compressor rotor and a turbine shaft portion connected to the turbine rotor; the compressor shaft portion and the turbine shaft portion connected axially together by a shaft coupling between the compressor rotor and the turbine rotor and at least a bearing rotatably coupled to the shaft assembly adjacent the shaft coupling; at least one of the compressor shaft and the turbine shaft being provided with openings between the bearing and the shaft coupling to permit cooling air to enter air passages in the area of the shaft coupling; and a source of pressurized cooling air in communication with the openings provided in the shaft assembly to direct such cooling air to the shaft coupling.
In a second aspect, there is provided a shaft assembly for a gas turbine engine of the type including at least a compressor rotor and a turbine rotor connected by the shaft assembly; the shaft assembly comprising a compressor shaft portion adapted to be connected to the compressor rotor and a turbine shaft portion adapted to be connected to the turbine rotor; the compressor shaft portion and the turbine shaft portion connected axially together by a shaft coupling arranged to be between the compressor rotor and the turbine rotor and the shaft assembly adapted to be rotatably coupled to at least a bearing adjacent the shaft coupling; at least one of the compressor shaft and the turbine shaft being provided with openings between the bearing and the shaft coupling to permit cooling air to enter air passages in the area of the shaft coupling.
Reference is now made to the accompanying figures in which:
Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below.
Referring to
Turbine shaft 30, which may be at a relatively high temperature due to its direct connection with the turbine rotor (not shown), may thus create thermal stresses within the compressor shaft 28, thus resulting in coning in the area of the interface of shaft 28 with the inner race 23a of bearing 23. This coning may result from the fact that the compressor stub shaft 28 is relatively cooler than the portion of the compressor shaft coupled to the hotter turbine stub shaft 30, especially since the bearing 23 is located in a very hot environment between the high pressure compressor 18 and the turbine 20.
As shown in more detail in
Alternatively, or additionally, cooling air may be brought to the spline 34 and thus to further surround stub shaft 30 with cool air, by allowing the bleeding of compressor air or externally cooled air to enter through a passage 56 in compressor shaft 28, on the forward side of the bearing housing 22. This pressurized cooling air can then follow a conduit defined between the shield 32 and the inner diameter of the high pressure compressor stub shaft 28 to then exit into this spline interface 34 by means of a passage 58 in the stub shaft 28.
It is pointed out that many of the components described above as being about the shafts 28 and 30 are annular. Accordingly, the various passages such as opening 48, opening 50, passage 56 and passage 58 may or many not be circumferentially distributed on the structural components in which they are defined.
The provision of pressurized cooling air through the shaft 24, particularly around the end of the turbine stub shaft 30 by way of the shaft coupling, such as the spline coupling 34, may contribute to the reduction of the thermal gradient at the compressor stub shaft 28 in the area of the bearing 23. This arrangement may reduce the occurrence of shaft or bearing race coning.
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.
