Shaft for use in an electric motor or generator

Abstract: A shaft for an electric motor includes axially distributed metallic (19) and nonmetallic (17) sections joined together. The shaft offers increased mechanical damping, increased rotor critical speed, improved corrosion resistance and improved motor performance.

Description: This invention relates to a shaft for use in an electric motor or generator. Conventional shafts for electric motors and generators are typically fabricated from metal and may include integrally formed rotors. Alternatively, the rotors may be separately formed. The rotors may include laminations, conductors, permanent magnets, etc. which constitute the rotating electromagnetic portion of the motor or generator. Typically the materials used in the shaft include steel or corrosion-resistant alloys. The damping properties, weight and other characteristics of the shaft are a function of the materials used for shaft construction. The aim of the present invention is to provide an improved shaft for an electric motor or generator. According to the present invention there is provided a shaft for use in an electric motor or generator, characterised in that said shaft comprises a plurality of axially distributed sections joined together including at least one metallic section and at least one nonmetallic section which is formed of a composite material. Further features of the invention are set out in Claim 2 et seq. For a better understanding of the present invention reference will now be made, by way of example, to the accompanying drawings, in which:- Fig. 1 is a side view partly in section, of part of a shaft in accordance with the invention wherein the composite body is shown in cross-section to illustrate the arrangement of the metallic and non-metallic sections; Fig. 2 is a side view, partly in section, of a shaft as in Fig. 1 having composite ribs; Fig. 3 is a side view of the metal end section of the shaft shown in Fig. 1; Fig. 4 is a side view, partly in section, of a shaft as in Fig. 1 provided with a removable sleeve with ribs; Fig. 5(a)-5(c) are a longitudinal sectional view and opposite end views, respectively of a removable sleeve similar to that shown in Fig. 4; Fig. 6 is a side view, partly in section, of a multi-section shaft in accordance with the invention; Fig. 7 is a side view of a metallic mid body section of the multi-section shaft shown in Fig. 6; Fig. 8 is a side view partly in section, of an electric motor shaft in accordance with the invention, the upper part of the figure showing the component before wrapping and the lower part of the figure showing the component after wrapping and finishing; and Fig. 9 is a longitudinal sectional view of an electric motor shaft in accordance with the invention with a separable rotor. Referring to Fig. 1 there is shown part of a shaft for an electric motor. The shaft, which is generally identified by the reference numeral 1 includes a metal end fitting 3 affixed at a joint 5 to a tubular composite body 7. The shaft 1 is assembled by pressing the metal end fitting 3 against one end of the tubular composite body 7 which is held in place with a composite threaded rod inserted through the center of the tubular composite body 7. Alternatively, the composite tubular body 7 may be held in place by inserting the tubular composite body 7 in the cavity of a filament winding machine. The tubular composite body 7 is molded and comprises high strength, high modulus fibers such as fiberglass, graphite, carbon, boron, quartz and aramyde fiber on a composite sleeve which is held against the metal end fitting 3. Preferably the tubular composite body is formed from S glass or carbon fiber. The tubular composite body 7 and the junction between the metal end fitting 3 and the tubular composite body 7 is then wrapped in fiber which is pre-impregnated with resin or fiber applied after passing through a resin bath. This fiber wrap produces a bridging tapered portion forming the joint 5 between the metal end fitting 3 and the tubular composite body 7. The fiber wrapped composite body is then cured and machined to size. Preferably the fiber materials used for wrapping are the same fiber materials used in the composite tubular body and includes carbon fiber and S glass fiber. As will be understood by those skilled in the art any suitable adhesive resin may be used depending on the environment of use. For example an epoxy resin is inexpensive and flexible while vinyl ester resins, which are not water soluble, may be preferred in an aqueous environment. Similarly a highly flame retardant resin may be used in a flammable environment. As shown in Fig. 2, an array of ribs 9 for supporting a rotor can be bonded to the shaft using a suitable epoxy or other adhesive. In this embodiment the ribs 9 are made of the same composite material as the material of the tubular composite body 7 although they could be made of a different material, for example, metal. A side view of the metal end fitting 3 is shown in Fig. 3. Typically the metal end fitting includes a stem portion 10 having segments of different diameters and an end 11 which is tapered at an angle of about 30° to the axis of the stem and includes flat facets 12 which engage the tubular composite body 7. Fig. 4 illustrates an alternate embodiment in which the ribs 9 are made of metal and are integral to a composite sleeve 13 which is removably retained on the tubular composite body 7 by metal retaining nuts 15. The sleeve 13 may also be made of metal. Figs. 5(a)-5(c) show such a metal sleeve which can be mounted on the tubular composite body 7. As best seen in the end views of Figs. 5(b) and 5(c) each end of the metal sleeve has flat surfaces 17 which are subsequently wrapped with fiber and machine finished. Fig. 6 illustrates another embodiment of the invention in which a multi-section motor shaft includes two nonmetallic shaft sections 18 formed of composite material and a metallic mid-body section 19. The nonmetallic shaft 18 sections help isolate upper and lower motor bearings from the driven component. While a shaft having two nonmetallic sections 18 and one metallic mid-body section 19 is illustrated in Fig. 6, it is clear to one skilled in the art that any arrangement of axially distributed metallic and nonmetallic sections may be provided. Fig. 7 illustrates a typical metallic mid-body section 19 of the type shown in Fig. 6 having a cylindrical portion 21 and tapered end portions 23 and 25. The several sections of the composite electric motor shaft according the to invention are preferably assembled prior to fiber wrapping. A typical motor shaft prior to fiber wrapping and finishing is shown in Fig. 8. The portion above the line A-A in Fig. 8 illustrates the preassembled shaft components including metal end pieces 27 which are placed in abutment against the composite body 29 and a metal sleeve 31 for receiving a rotor mounted on the composite body 29. After assembly of these metal and composite body components the entire shaft is wrapped with fiber in the manner described above and machine finished. The portion below line A-A depicts the motor shaft after fiber wrapping and machine finishing. Portions of the shaft marked in cross hatch 33 indicate fiber wrapped portions. The metal end pieces 35 and sleeve 37 are machine finished to suitable shapes. An assembled motor shaft and rotor in accordance with the invention is shown in Fig. 9. A removable metal rotor 39 is mounted on a metal sleeve 41 having ribs, the metal sleeve being inserted on the composite sleeve 43. Tapered end sleeves formed of metal 45 additionally secures and supports metal sleeve 41. The nonmetallic sections of the electric motor shaft and rotor described herein provide reduced weight and rotational inertia as compared to shafts constructed entirely of metal. The nonmetallic sections also provide increased damping, thereby increasing overall damping of shaft-borne vibrations. The increased damping is highly desirable as in minimizes the detrimental forces imparted by the motor on the driven component as well as by the driven component on the motor bearings. The use of composite materials alters the inertia and stiffness in the shaft resulting in greater absorption of vibration. As a result of the mechanical properties of the composite material a higher critical motor speed is achievable. In this regard increasing the critical motor speed so as to exceed the start and run frequency range results in less trauma to the motor and a driven component resulting from motor and a driven component natural frequency excitation. The electric motor shaft according to the invention also exhibits improved corrosion resistance since the nonmetallic sections are inert in most environments whereas metallic shafts made of various steel, nickel or other metals may be subject to corrosion in certain environments. In addition, the use of multi-section motor shafts facilitates fabrication of motor shafts with complex geometries and allows variation of motor shaft damping along the shaft length to further attenuate vibratory energy. By varying thickness and winding geometry the composite body may be used to provide desired shaft strength, stiffness and damping characteristics. By making the rotor separable from the shaft, repair and replacement of the shaft is facilitated. Shafts in accordance with the present invention are particularly suitable for use in electric motors having a power output of from 2 to 70,000 shaft horsepower (1496 to 5.1×10 7 KW).

Claims: A shaft for use in an electric motor or generator, characterised in that said shaft comprises a plurality of axially distributed sections (3, 7) joined together including at least one metallic section (3) and at least one nonmetallic section (7) which is formed of a composite material. A shaft as claimed in Claim 1, comprising a shaft body section (7) formed of composite material and a metallic shaft end section (3) affixed to one end of the shaft body section (7). A shaft as claimed in Claim 2, comprising longitudinally extending ribs (9) affixed to the outer surface of the shaft body section (7) wherein the ribs (9) are formed of composite material. A shaft as claimed in Claim 2, including a sleeve (13) removably mounted on the surface of the shaft body section (7) and longitudinally extending ribs (9) on the sleeve. A shaft as claimed in Claim 4, wherein the sleeve (13) is formed of composite material and the ribs (9) are formed of metal. A shaft as claimed in any preceding claim, comprising at least two metallic sections (19) and at least two nonmetallic sections (18) in alternating arrangement in the axial direction of the shaft. A shaft as claimed in any preceding claim, wherein the composite material comprises a material selected from the group consisting of filament wound carbon fiber and glass fibers. A shaft as claimed in any preceding claim provided with a rotor. A shaft as claimed in Claim 8, wherein said rotor is removably mounted on said shaft. An electric motor or generator provided with a shaft as claimed in any preceding claim.

Inventors: DINE PIET VAN, HARRING WILLIAM R, ODESSKY VLADIMIR, SMITH JAMES S, SPENCER BRIAN E, HARRING, WILLIAM R., ODESSKY, VLADIMIR, SMITH, JAMES S., SPENCER, BRIAN E., VAN DINE, PIET
Applicants: ELECTRIC BOAT CORP, ELECTRIC BOAT CORPORATION
Application year: 1998
Main classification: H02K7
IPC codes: F16C3, H02K1, H02K7