BACKGROUND OF THE INVENTION

[0001] In rotating machinery, such as electric rotary machines or turbo- machinery, axial (thrust) magnetic bearings are used to provide non-contact levitation in the axial direction. As shown in Figs. 1 and 2, a conventional axial magnetic bearing 8 has solid stators 10 and a solid rotor 12, each composed of a magnetically- permeable material. The rotor 12 is secured to a rotatable shaft 14. Typically, one or more circular grooves are formed in the stators 10, and circular coils 16 are inserted in the grooves, respectively. Each groove is coaxial with the shaft 14. This construction causes eddy currents to be induced in both the rotor 12 and the stators 10. The induced eddy currents inhibit a change of magnetic flux, thereby limiting the bandwith of the axial magnetic bearing 8, which limits dynamic performance. As a result, a conventional axial magnetic bearing is over- dimensioned to satisfy the dynamic force requirement at high frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] The features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:

[0003] Fig. 1 is a side sectional view of a prior art axial magnetic bearing;

[0004] Fig. 2 is an inner end view of a stator of the prior art axial magnetic bearing;

[0005] Fig. 3 is a side sectional view of a first axial magnetic bearing

constructed in accordance with a first embodiment of the present invention;

[0006] Fig. 4 is an inner end view of a stator of the first axial magnetic bearing of the present invention;

[0007] Fig. 5 is a sectional view of a rotor of the first axial magnetic bearing of the present invention, taken along the plane B-B in Fig. 3;

[0008] Fig. 6 is a sectional view of the rotor of the first axial magnetic bearing of the present invention, taken along the plane A-A in Fig. 3;

[0009] Fig. 7 is a side sectional view of a second axial magnetic bearing constructed in accordance with a second embodiment of the present invention;

[00010] Fig. 8 is a side sectional view of a third axial magnetic bearing constructed in accordance with a third embodiment of the present invention; and

[00011] Fig. 9 is a side sectional view of a fourth axial magnetic bearing constructed in accordance with a fourth embodiment of the present invention

BRIEF DESCRIPTION OF INVENTION

[00012] It should be noted that in the detailed description that follows, identical components have the same reference numerals, regardless of whether they are shown in different embodiments of the present invention. It should also be noted that in order to clearly and concisely disclose the present invention, the drawings may not necessarily be to scale and certain features of the invention may be shown in somewhat schematic form.

[00013] In accordance with the present invention, an improved axial magnetic bearing 20 for a rotating machine is provided. The axial magnetic bearing 20 addresses deficiencies in the prior art. Referring now to Figs. 3-6, the axial magnetic bearing 20 generally includes a rotor 22 disposed between a pair of stators 24. It should be appreciated, however, that in other embodiments, the rotor 22 may be disposed next to a single stator 24.

[00014] The rotor 22 is secured to a rotatable shaft 26 and is formed from layers (or laminations) of magnetically permeable material, such as carbon steel, silicon steel or amorphous metal. One or more strips or sheets of the magnetically- permeable material may be wound onto the shaft 26 to form a roll comprised of turns or layers of the magnetically-permeable material. The layers are arranged one on top of the other in a radial direction and are secured to the shaft 26 by a plurality of radially-extending bolts 30, which are composed of a non-conductive material. The bolts 30 extend through the layers and into the shaft 26, with ends of the bolts 30 being securedly held in the shaft 26. In addition, an outer retaining sleeve 32 may be disposed over the roll of layers to prevent relative movement of the layers in an axial or circumferential direction. The retaining sleeve 32 is composed of a non-magnetic material, such as a fiber-reinforced dielectric plastic or stainless steel.

[00015] The stators 24 are mounted so as to be fixed in position. The shaft 26 extends through center openings in the stators 24 so as to be rotatably and axially moveble relative to the stators 24. Each stator 24 is also formed from layers (or laminations) of magnetically- permeable material, such as carbon steel, silicon steel or amorphous metal. One or more strips or sheets of the magnetically-permeable material may be wound to form a roll comprised of turns or layers of the

magnetically-permeable material. The layers are arranged one on top of the other in a radial direction. The layers may be secured to a stator frame (not shown) by a plurality of radially-extending bolts, which are composed of a non-conductive material. The bolts extend through the layers and into the stator frame, with ends of the bolts being securely held in the stator frame. A plurality of endless grooves are formed in an inner or first end of each stator 24. Each groove is generally kidney- shaped and is not co-axial with the shaft 26. Instead, the grooves in each stator 24 are circumferentially spaced-apart in a circular configuration that is co-axial with the shaft 26. In each stator 24, the grooves are aligned in the axial direction of the shaft 26, i.e., are disposed in the same radial plane. The grooves may be formed by machining after the stators 24 have been wound and/otherwise formed. A coil 36 is mounted inside each groove. The coils 36 are formed from one or more lengths of a conductive material, such as copper, and are connected to a source of power. The power to each coil 36 may be provided from separate amplifiers that are separately controllable. In Fig. 4, four grooves and four coils 36 are shown. More or fewer grooves and coils 36 may be provided. The grooves and coils 36 of the stators 54 face the rotor 22. Thus, each end of the rotor 22 faces a plurality of coils 36.

[00016] Referring now to Fig. 7, there is shown an axial magnetic bearing 50 constructed in accordance with a second embodiment of the present invention. The axial magnetic bearing 50 includes a single fixed stator 52 disposed between two rotors 22 secured to the shaft 26. The stator 52 has the same construction as the stator 24, except the stator 52 has a plurality of endless grooves formed in both first and second ends of the stator 52, with a coil 36 being mounted in each groove. In this manner, the grooves and the coils 36 in the first and second ends face the rotors 22, respectively. In each of the first and second ends of the stator 52, the endless grooves are formed in the same manner and have the same configuration as shown in Fig. 4 and as described above.

[00017] Referring now to Fig. 8 there is shown an axial magnetic bearing 60 constructed in accordance with a third embodiment of the present invention. The axial magnetic bearing 60 includes a single fixed stator 62 disposed between two rotors 64 secured to the shaft 26. The stator 62 has the same construction as the stator 24, except the stator 62 has no grooves formed therein and no coils 36. Each rotor 64 has the same construction as the rotor 22, except each rotor 64 has a plurality of endless grooves formed in an inner or first end of each rotor 64. A coil 36 is mounted in each of the grooves. With the grooves and the coils 36 being formed in the inner ends of the rotors 64, the coils 36 in each rotor 64 face the stator 24. In each of the rotors 64, the endless grooves are formed in the same manner and have the same configuration as shown in Fig. 4 and as described above.

[00018] Referring now to Fig. 9 there is shown an axial magnetic bearing 70 constructed in accordance with a fourth embodiment of the present invention. The axial magnetic bearing 90 includes a plurality of fixed stators and a plurality of rotors 22 secured to the shaft 26. Three rotors 22 and four stators are shown in Fig. 9. The rotors 22 and the stators are arranged in alternating manner, with each rotor 22 being disposed between a pair of stators. The stators include a pair of stators 52 described above in the second embodiment and a pair of stators 24 described above in the first embodiment. The stators 24 are disposed outward from, and bracket, the rotors 22 and the stators 52. With the foregoing arrangement, each end of each rotor 22 faces a plurality of coils 36.

[00019] It should be appreciated that axial magnetic bearings having multiple rotors and multiple stators, but with different numbers of rotors and stators and different arrangements may be provided without departing from the scope of the present invention.

[00020] It should further be appreciated that in other embodiments of the present invention, each rotor 22, 64 and/or each stator 24, 52, 62 may be only partially constructed of layers of magnetic material. More specifically, each rotor 22, 64 and/or each stator 24, 52, 62 may include one or more portions composed of a solid material and one or more other portions comprised of layers of magnetic material. The solid material may be magnetic or non-magnetic. For example, each rotor 22, 64 and each stator 24, 52, 62 may include a radially-inner portion

composed of cast carbon steel and a radially-outer portion comprised of layers of silicon steel and/or amorphous metal. In each of the axial magnetic bearings 20, 50, 60, 70, one or more position sensors (not shown) are provided to detect the displacement of each rotor (22 or 64) in the axial direction. One or more

displacement signals from the one or more sensors are transmitted to a digital controller that is connected to the amplifier(s). Based on the displacement signal(s), the controller sends one or more control signals to the amplifier(s) to adjust the current in the coils 36. In this manner, electromagnetic force is generated by the coils 36 to control the axial position of each rotor (22 or 64).

[00021] In each of the axial magnetic bearings 20, 50, 60, 70, electromagnetic flux travels in the axial and circumferential directions. Thus, induced eddy currents are significantly reduced, thereby improving dynamic performance. Another benefit of the axial magnetic bearings 20, 50, 60, 70 is fault tolerance. Since multiple coils 36 are used in each stator (24, 52) and/or each rotor 64, each axial magnetic bearing 20, 50, 60, 70 can still provide partial axial force even if some of the coils 36 fail. The provision of multiple amplifiers further increases redundancy.

[00022] It is to be understood that the description of the foregoing exemplary embodiment(s) is (are) intended to be only illustrative, rather than exhaustive, of the present invention. Those of ordinary skill will be able to make certain additions, deletions, and/or modifications to the embodiment(s) of the disclosed subject matter without departing from the spirit of the invention or its scope, as defined by the appended claims.