RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Serial No. 61/383,063, filed September 15, 2010, and entitled "Method and

Apparatus for Connecting Turbine Rotors," which is incorporated herein by reference in its entirety for all purposes.

TECHNICAL FIELD

This invention relates to connecting rotors in rotary machines, particularly turbines.

BACKGROUND

Typical gas turbines include several stages, with each set of turbine blades being associated with a corresponding stage. Each set of turbine blades is generally attached to a corresponding central disc, which are in turn attached to a central shaft and/or to adjacent discs of the turbine assembly. When connected together, the sets of turbine blades rotate together as a single multistage unit.

SUMMARY OF INVENTION

Prior turbine assemblies generally attach individual turbine rotors together by bolts, clips, pins, curvic or Hirth couplings, and/or other arrangements. These coupling arrangements can in some cases complicate the manufacture of turbine rotors and/or the assembly of rotors into a multistage unit.

Some aspects of the invention provide for a simplified attachment of rotors to each other and/or other components of a turbine assembly, such as a drive shaft. In one illustrative embodiment, rotors may be attached together (or attached to a drive shaft or other turbine assembly component) by only a friction fit. The friction fit engagement may be suitable to maintain attachment of the rotors (or rotor and shaft) during normal operation of the turbine assembly. For example, in the case of some gas turbine assemblies, the friction fit attachment may be suitable to withstand (i.e., maintain attachment of the rotors or rotor/shaft for) rotary speeds of up to about 26,000 rpm, to withstand torques between the rotors or rotor/shaft that are typically experienced in gas turbines, to withstand temperatures up to about 1400 degrees Celsius, and so on. In other words, the friction fit may be suitable to maintain connection between rotors or a rotor and shaft for a full range of turbine operating conditions. Such an arrangement may provide advantages when connecting ceramic rotors together (e.g., discs or blisks made entirely of a ceramic material). That is, ceramic materials can be prone to stress fractures or other damage that may be caused by holes, notches or other features often used to connect rotors to each other. Illustrative embodiments may allow for the proper connection of rotors while avoiding the need for such features. (As used herein, a turbine "rotor" refers to an arrangement that includes a disc with one or more blades attached to the disc. The disc and blades may be made as a single unitary part, e.g., by molding, sintering, etc., or may be made as two or more separate parts that are attached together, e.g., by welding, bolting, cementing, interference fit, or other engagement. Thus, a "rotor" as used herein refers to a "blisk", or unitary blade and disc arrangement, as well as multipart blade and disc arrangements.)

In one embodiment, a friction fit attachment between rotors may be provided by a self- locking tapered fit joint. For example, the rotors may include complementary engagement surfaces that are arranged so that when the surfaces are placed into contact, the surfaces attach the rotors together in a way suitable for withstanding normal operating conditions for the rotors. In one embodiment, the rotors may include annular surfaces (e.g., surfaces that are portions of the outer surface of a cone, sphere or cylinder) that are tapered and engage such that one surface is received by the other in male/female arrangement.

In some embodiments, the rotors may be boreless, i.e., the rotors may be arranged in a turbine assembly such that no central drive shaft or other member passes axially through the rotors. Such an arrangement may be useful in relatively high temperature applications where a metallic shaft may not be capable of withstanding normal operating temperatures at or near the rotors. Moreover, manufacture and assembly of the rotors into a multistage arrangement may be simplified because of the lack of any need to accommodate a central shaft on which to mount the rotors. In some embodiments, the rotors may be completely free of any holes or openings arranged in an axial direction. That is, since the rotors may be attached together by way of a friction fit only, there may be no need to provide the rotors with any axial holes to receive bolts, clips, pins, shafts or other components typically used to attach rotors together (or to attach rotors to a drive shaft). This may enable the use of ceramic materials in some applications that were previously not possible. That is, ceramic rotors often do not function well when holes, notches or other features that may cause thermal or other stress concentrations in the material. However, prior rotor connection arrangements typically rely on such features, making the use of ceramic materials difficult or impossible in some cases.

Although embodiments of the invention involve the use of a friction fit attachment suitable to withstand operating conditions of a turbine assembly, friction fit attachments in accordance with aspects of the invention may be used together with other rotor attachment, such as bolts, pins, clips, etc. For example, a friction fit attachment may be used to initially attach two turbine rotors together when assembling the rotors. This initial attachment may free a technician's hands or otherwise allow a technician to engage other attachments between the rotors while the friction fit holds the rotors together. In one embodiment, a technician may mount a second rotor to a first rotor by way of a friction fit, and then release the second rotor (e.g., by removing his hands, releasing a crane from the second rotor, etc.), allowing the friction fit alone to maintain engagement of the rotors. Since the friction fit may maintain the second rotor attached to the first rotor (at least temporarily), the technician may be able to make fine adjustments to the position of the second rotor relative to the first rotor and/or to engage bolts, pins, clips, etc. with the first and second rotors to establish a more permanent connection. The friction fit may also provide an alignment function, e.g., align the first and second rotors so that a center of mass for the two rotors lies on a desired axis or other suitable location.

These and other aspects of the invention will be apparent from the following description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. In the figures: FIG. 1 is an exemplary schematic diagram of a turbine assembly, according to some embodiments;

FIG. 2 is, according to some embodiments, a cross-sectional schematic diagram of rotors; FIG. 3 is a cross-sectional schematic diagram illustrating the attachment of rotors to components of a turbine assembly, according to one set of embodiments;

FIG. 4 is a cross-sectional schematic diagram of rotors, according to some embodiments; FIG. 5 is, according to some embodiments, a cross-sectional schematic diagram of three rotors;

FIG. 6 is an exemplary schematic diagram illustrating a connection between a stub shaft and a rotor, according to some embodiments; and

FIG. 7 is an exemplary schematic diagram, according to some embodiments, illustrating a connection between a stub shaft and a rotor.

DETAILED DESCRIPTION FIG. 1 shows an illustrative embodiment of a turbine assembly that incorporates one or more aspects of the invention. In this embodiment, the turbine assembly 1 includes a pair of rotors 2, 3 that have complementary engagement surfaces suitable to form a friction fit or engagement of the rotors 2, 3. The rotors 2, 3 each include a disc 4 that has one or more blades 5 attached to the disc 4. (The term "disc" is used herein to refer to a member that connects two or more blades together, but is not necessarily limited to a disk, or disk-like shape. To the contrary, a "disc" as used herein may take any suitable shape, size or other configuration so as to function in a turbine assembly.) The rotors 2, 3 may be made in any suitable way, such as by molding, sintering, or otherwise forming the disc 4 and blades 5 as a single, unitary part (e.g., to form a "blisk"), or by forming the disc 4 and/or blades 5 as one or more separate parts and assembling the parts together to form a rotor 2, 3. In one illustrative embodiment, the rotors 2, 3 are formed as a blisk having a diameter of up to about 14.5 inches or more. The blisks may be formed of a ceramic material, such as silicon carbide or silicon nitride (S1 ₃ N ₄ , or SiN), of a metal material, or of a combination of suitable materials. If made of silicon nitride material, the rotors 2, 3 (or portions thereof) may be made using a hot isostatic pressed (HIP) process. If the rotors 2, 3 are assembled from multiple parts, a variety of different materials may be used. For example, the disc 4 may be made of a metal material and the blades 5 made of a ceramic material with the blades 5 attached to the disc 4 by welding, adhesive, mechanical connectors, interlocking geometry, etc. Further, the disc 4 and blades 5 may have any size, shape, surface finish, size tolerance, cooling passages, or other configuration for use in any type of turbine assembly, whether for operation as an engine, compressor, a dual purpose, or other arrangement.

In the embodiment shown in FIG. 1, the first and second rotors 2, 3 include engagement surfaces 6 that are complementary with each other such that the first and second rotors 2, 3 may be attached to each other by a friction fit of the engagement surfaces 6. In this embodiment, the engagement surfaces 6 have an annular shape, e.g., have a shape of the outer surface of a cylinder, cone, sphere or other suitable shape. The engagement surfaces 6 may be arranged to provide a self-locking, tapered fit joint when the engagement surfaces 6 are placed into contact with each other. For example, FIG. 2 shows a cross sectional view of the rotors 2, 3 with the engagement surfaces 6 in fractional engagement with each other. As can be seen in FIG. 2, the engagement surface 6 of the first rotor 2 may be tapered such that the diameter or size of the engagement surface decreases with increasing distance from the disc 4. The engagement surface 6 of the second rotor 3 may be tapered such that the diameter or size of the engagement surface 6 increases with increasing distance from the disc 4. Thus, the engagement surface 6 of the first rotor 2 (a male engagement surface) may be received by the engagement surface 6 of the second rotor 3 (a female engagement surface) such that the rotors 2, 3 can only be separated by exerting a positive extraction force to the rotors 2, 3, e.g., by exerting forces in the axial direction to separate the rotors 2, 3. The engagement surfaces 6 may have a relatively low included angle, e.g., where the engagement surfaces 6 have the shape of a portion of a cone, so as to provide a self-locking feature.

In this embodiment, the engagement surfaces 6 extend in a direction generally axially away their respective discs 4, but may be arranged in other ways, e.g., so as to extend axially into a respective disc 4 to form a groove in the disc 4. Also, in this illustrative embodiment, the engagement surfaces 6 are generally located at or near a "free ring stress" radius or other location of the rotor 2, 3. The "free ring stress" radius is a location where the disc expands under rotational stress at the same rate as does a free ring of the same material and thus reduces a stress that may be created between rotors 2, 3 at the engagement surfaces 6. It should be understood, however, that the engagement surfaces 6 may be arranged in other ways, e.g., the surfaces 6 may be arranged at locations other than the "free ring stress" location, multiple engagement surfaces 6 may be provided for each rotor 2, 3 (e.g., multiple concentric engagement surfaces 6 may be provided for each rotor 2, 3), the engagement surfaces 6 may include multiple discrete surfaces instead of a single, continuous surface like that in FIGs. 1 and 2, and so on. For example, rather than have the engagement surfaces 6 of the rotors 2, 3 in FIGs. 1 and 2 be arranged to have a continuous surface with a conical shape, the engagement surfaces 6 may be broken up into multiple discrete portions.

In this illustrative embodiment, the rotors 2, 3 are boreless, or have no opening arranged to receive central drive shaft or other member that passes axially through the rotors. Such an arrangement may simplify manufacture of the rotors 2, 3, e.g., because a properly located central opening need not be formed in the rotors 2, 3. Further, in these embodiments the rotors 2, 3 include no openings or other features used to receive bolts, pins, clips or other arrangements to fasten the rotors 2, 3 together. Instead, the friction fit attachment provided by the engagement surfaces 6 may be the only physical attachment between the rotors 2, 3. However, in other embodiments, the friction fit attachment of the engagement surfaces 6 may supplemented by bolts, clips, pins, etc. As discussed above, the engagement surfaces 6 may provide a temporary attachment between the rotors 2, 3, e.g., that permits a technician to make fine rotational or other position adjustments of the rotors 2, 3 prior to final fixation by bolts, clips or other fasteners. Alternately, the engagement surfaces 6 may provide an alignment function that helps to properly align the rotors 2, 3 relative to each other while maintaining at least a temporary friction fit engagement.

Although only two rotors 2, 3 are shown attached together in FIGs. 1 and 2, stacks of multiple rotors may be attached together in a multistage turbine assembly. For example, the first rotor 2 shown in FIG. 2 has an engagement surface 6 on a side opposite the second rotor 3 (i.e., on the left as shown in FIG. 2) that may be used to engage the first rotor 2 to another rotor in a same way that the first and second rotors 2, 3 are attached together. Similarly, the second rotor 3 includes an engagement surface 6 on a side opposite the first rotor 2, (i.e., on the right as shown in FIG. 2) that may be used to engage with another rotor. Thus, a multistage rotor assembly may be assembled without the need for center holes (e.g., for rotor alignment) or curvic or other couplings (e.g., for alignment and/or torque transmission between rotors). For example, FIG. 5 includes an exemplary schematic illustration of a system in which three rotors 2, 3, and 7 form a multistage rotor assembly. Furthermore, the engagement surfaces 6 may be used to attach a rotor 2, 3, or an assembly of such rotors, to a drive shaft, or other portion of a turbine assembly. For example, FIG. 3 shows the rotors 2, 3 attached on the left side to a drive shaft and on the right side to a bearing support by way of engagement surfaces 6 on the rotors 2, 3. In this embodiment, the drive shaft includes a stub shaft or other component that includes an engagement surface 6 that is complementary to the engagement surface on the left side of the rotor 2. Similarly, a second stub shaft engages with the second rotor 3 by way of an engagement surface 6 to provide a rotary bearing support to the rotor assembly on a right side of the assembly. The friction fit

engagement of the rotors 2, 3 with the drive shaft may be suitable to couple the rotors 2, 3 with the drive shaft so as to transmit torque with little or no slip. In this embodiment, the stub shafts are made of a ceramic material, whereas the remainder of the drive shaft may be made of a metal material, but other arrangements are possible. The rotors and the stub shaft can be engaged in any suitable configuration. For example, as shown in FIG. 6, portion 10 of the stub shaft engaged with the rotor can be located outside tapered rotor engagement portion 11, relative to the axis around which the rotor rotates. In some embodiments, portion 10 of the stub shaft engaged with the rotor can be located inside tapered rotor engagement portion 11, relative to the axis around which the rotor rotates, as illustrated in FIG. 7. In some cases, configuring stub shaft engagement portion 10 to be inside tapered rotor engagement portion 11 (as illustrated in FIG. 7) can reduce the amount of stress imparted to the stub shaft and/or the tapered rotor engagement portion, leading to enhanced performance.

The engagement surfaces 6 may be arranged suitable ways other than that shown in FIGs. 1 and 2. For example, FIG. 4 shows a cross sectional view of an illustrative embodiment in which a first engagement surface 6a is formed by an axially extending rib, and a second engagement surface 6b is formed by an axially extending groove. The first and second engagement surfaces 6a and 6b are complementary such that the second engagement surface 6b receives the first engagement surface 6a, e.g., with frictional engagement. The surfaces 6a and 6b may have tapered portions that provide a self-locking taper like that in FIGs. 1 and 2, or may be arranged in other ways. For example, in this embodiment, the engagement surfaces 6a and 6b include circumferential grooves (e.g., having a half round shape) that align with each other when the surfaces 6a and 6b are engaged. The grooves may be filled with an adhesive, cement or other material that cures or otherwise hardens after assembly of the rotors to provide a bond between the rotors. The adhesive bond may supplement a friction fit between the engagement surfaces 6a and 6b. (It should be understood that a similar groove feature may be provided with the engagement surfaces 6 in the FIGs. 1 and 2 embodiment, if desired.)

U.S. Provisional Patent Application Serial No. 61/383,063, filed September 15, 2010, and entitled "Method and Apparatus for Connecting Turbine Rotors" is incorporated herein by reference in its entirety for all purposes.

While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or

configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, and/or methods, if such features, systems, articles, materials, and/or methods are not mutually inconsistent, is included within the scope of the present invention.

The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one."

The phrase "and/or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to "A and/or B," when used in conjunction with open-ended language such as "comprising" can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

As used herein in the specification and in the claims, "or" should be understood to have the same meaning as "and/or" as defined above. For example, when separating items in a list, "or" or "and/or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as "only one of or "exactly one of," or, when used in the claims, "consisting of," will refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be interpreted as indicating exclusive alternatives (i.e. "one or the other but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of," when used in the claims, shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc. In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of and "consisting essentially of shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

What is claimed is: