Patent Application
20110146298
The present invention relates to retaining members, and more particularly to retaining members configured for use with shafts of gas turbine engines and associated assembly methods.
Machines such as gas turbine engines often include stacks of rotatable parts that must be held together during operation. Tie shafts and threaded retaining nuts are commonly used to hold together, and in some instances axially compress, rotor stacks in gas turbine engines. The operating envelope of a typical gas turbine engine can generate significant forces and temperatures, which can cause certain components to deform. Under such conditions the retaining nut can exhibit undesirable “lift-off”, or may loosen or otherwise undesirably reduce its effectiveness in holding the rotor stack together. In particular, a forward portion of the retaining nut tends to exhibit lift-off.
Thus, the present invention provides an alternative retaining member suitable for use in a gas turbine engine, and an alternative method of assembly.
A gas turbine engine assembly according to the present invention includes a rotor shaft having a threaded portion, a rotor stack support positioned radially outward from the rotor shaft, and a locking nut. The locking nut includes a body portion, a threaded portion located on a radially inner surface of the body portion, and a lug portion extending from the body portion. The rotor stack support radially rests upon the body portion of the locking nut, and the rotor stack support axially rests against the lug portion of the locking nut. The threaded portion of the locking nut and the threaded portion of the rotor shaft are engaged together.
In general, the present invention relates to a retaining member or locking nut, a gas turbine engine assembly having such a retaining member, and a method of assembly for a gas turbine engine. The retaining member is threadably engaged on a rotor shaft (or tie shaft). The retaining member axially abuts a support member, such as a frusto-conical stub shaft or other rotor stack support, and the support member radially rests on the retaining member to restrain and limit lift-off during engine operation. The retaining member and the support member can include cooperative castellations (i.e., teeth) and notches that are engaged to effectively lock the retaining member in place by reducing or eliminating rotation of the retaining member relative to the support member. During assembly, the rotor shaft can be stretched to create a rotor stack axial preload force on the support member for torque transmission and permit threading the retaining member on the rotor shaft, and the rotor shaft then released (i.e., unstretched) to apply the preload force to the rotor stack and to engage the castellations and notches. Additional features and benefits of the present invention will be recognized in view of the description that follows.
The retaining member 30 includes a substantially cylindrical body portion 40, a threaded portion 42, a lug portion 44, a forward pilot 46, an aft pilot 48, a land 50, and a stress relief groove 52. In the illustrated embodiment, one half of the retaining member 30 viewed in cross-section is generally L-shaped. The forward pilot 46 is located at a forward end of the body portion 40 and the aft pilot 48 is located at an opposite aft end of the body portion 40 such that the pilots 46 and 48 are axially spaced from each other. Pilots 46 and 48 both face radially inward, and can protrude slightly from the body portion 40. The threaded portion 42 is located at a radially inner surface of the body portion 40, and is axially arranged in between the pilots 46 and 48. The land 50 can extend in a substantially annular shape. The land 50 is positioned at a radially outer surface of the body portion 40, and can be axially aligned with the threaded portion 42. The lug portion 44 is located at or near the aft end of body portion 40, and extends generally radially outward. As shown in
The shaft 26 includes a threaded portion 58. The threaded portion 42 of the retaining member 30 is configured to engage the threaded portion 58 of the shaft 26. A land 60 is located forward of the threaded portion 58 and extends radially outward from the shaft 26. The forward pilot 46 of the retaining member 30 can fit about the land 60, and that fit can be line-on-line or slightly loose to help enable assembly while ensuring that the threaded portions 42 and 58 can be centered relative to each other. The aft pilot 48 of the retaining member 30 loosely rests on shaft 26 aft of the threaded portion 58. An additional land can optionally be provided where the aft pilot 48 rests upon the shaft 26. As shown in
The surface 34 of the rotor stack support 28 rests against the retaining member 30 and can thereby contact and exert force upon the land 50 to restrain and limit displacement and deflection of the retaining member 30 relative to the shaft 26, which helps reduce lift-off of the retaining member 30. More particularly, the rotor stack support 28 can be axially positioned such that the surface 34 helps maintain engagement of the threaded portion 42 of the retaining member 30 with the threaded portion 58 of the shaft 26. As shown in the illustrated embodiment, the pilots 46 and 48 are axially spaced from the surface 34 at opposite sides of the land 50 so that distribution of the load on the retaining member 30 exerted by the rotor stack support 28 (after unstretching of the shaft 26) is pointed to help counteract the tendency for lift-off of the retaining member 30 during operation of the engine 10. A fit between the surface 34 of the rotor stack support 28 and the land 50 on the shaft 26 can be selected as a function of required operating conditions, and can be a relatively tight fit. As axial loading increases on the threaded portions 42 and 58, for higher torque driven gas turbine engines, the lift-off effect is greatly reduced on the first few threads of the threaded portions 42 and 58.
When the retaining member 30 is tightened and the shaft 26 is unstretched (as explained below), the engagement surface 54 on the lug portion 44 of the retaining member 30 abuts and axially presses against the surface 36 of the rotor stack support 28. This allows the retaining member 30 to provide a compressive force to the rotor stack support 28, which can help hold together a stack of components connected to the rotor stack support 28. For instance, the retaining member 30 can compress the rotor stack support 28 against components of the HPC 16, or other rotor stacks in the engine 10. While the engagement surface 54 and the surface 36 are in contact, the castellations 38 can be configured so as not to bottom out in the notches 56. In other words, the notches 56 can have an axial depth that is greater than an axial length of the castellations 38. Such a configuration causes loads on the rotor stack support 28 to be borne through the surface 36 rather than through the castellations 38. Furthermore, the axial length of the castellations 38 is generally proportional to a length of shaft stretch for the shaft 26 as the mating engagement of the castellations 38 with the notches 56 is related to shaft stretching, as will be explained further below. The castellations 38 help to prevent relative circumferential rotation, about the engine centerline CL, between the retaining member 30 and the rotor stack support 28.
It should be noted that terms of orientation used herein like “forward” and “aft” are relative. In alternative embodiments those relative orientations can vary as desired for particular applications. Moreover, while the illustrated embodiment depicts the castellations 38 on the rotor stack support 28 and the notches 56 on the retaining member 30, in alternative embodiments the locations of those features on the rotor stack support 28 and the retaining member 30 can be reversed or otherwise relocated.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. For example, the retaining member or locking nut of the present invention can be utilized in a variety of locations within a gas turbine engine, such as adjacent to an HPT stack, as well as with a variety of other machines and apparatuses.
