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An electrical submersible well pump assembly includes a rotary pump and a motor. An inner rotor is coupled to the motor shaft. The inner rotor has steel discs stacked together with end caps at each end. The discs have apertures that align to define axially extending slots. Each of the slots has a cl

An electrical submersible well pump assembly includes a rotary pump and a motor. An inner rotor is coupled to the motor shaft. The inner rotor has steel discs stacked together with end caps at each end. The discs have apertures that align to define axially extending slots. Each of the slots has a closed outer wall spaced radially inward from an outer diameter surface of the inner rotor. Inner rotor magnets are located within the slots. Continuous open and thin gaps between rotating components act as hydrodynamic bearings. Damper bars extend axially at points between the outer walls of the slots and the outer diameter surface of the inner rotor. An outer rotor has a bore that receives the inner rotor, the outer rotor being operatively coupled to the pump shaft for rotation therewith. Outer rotor magnets are mounted to the bore of outer rotor.

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1. An electrical submersible well pump assembly, comprising: a rotary pump having a rotatable pump shaft;a motor having a motor shaft that is rotated by the motor and extends along an axis of the pump assembly;a magnetic coupling unit, comprising:an inner rotor operatively coupled to one of the pump

1. An electrical submersible well pump assembly, comprising: a rotary pump having a rotatable pump shaft;a motor having a motor shaft that is rotated by the motor and extends along an axis of the pump assembly;a magnetic coupling unit, comprising:an inner rotor operatively coupled to one of the pump or motor shafts for rotation therewith, the inner rotor having a plurality of slots therein, each of the slots having an outer wall spaced radially inward from an outer diameter surface of the inner rotor;a plurality of inner rotor magnets, each located within one of the slots;an outer rotor surrounding the inner rotor and operatively coupled to the other of the pump or rotor shafts for rotation therewith;a plurality of outer rotor magnets mounted to the outer rotor to attract magnetic fields of the inner rotor magnets and cause the inner and outer rotors to rotate in unison;a plurality of non magnetic, electrically conductive damper bars, each of the damper bars extending through the inner rotor between at least one of the inner rotor magnets and the outer diameter surface of the inner rotor, the damper bars being spaced around and parallel to the axis; and whereineach of the slots has side edges that extend outward from the inner rotor magnet contained therein toward but not completely to the outer diameter surface of the inner rotor, defining flux barrier cavities, at least one of the damper bars being located between the flux barrier cavities of one of the slots. 2. The assembly according to claim 1, wherein: each of the inner rotor magnets has an outer side that is flat and faces radially outward from the axis. 3. The assembly according to claim 1, wherein: at least two of the damper bars are located between each of the inner rotor magnets and the outer diameter of the inner rotor. 4. The assembly according to claim 1, wherein the inner rotor comprises: a plurality of discs stacked together, each of the discs being of a magnetic material and having apertures that define the slots. 5. The assembly according to claim 1, further comprising: end caps at opposite ends of the inner rotor; andwherein each of the damper bars has opposite ends secured to the end caps. 6. The assembly according to claim 1, wherein: each of the inner rotor magnets has parallel flat inner and outer sides; andeach of the outer rotor magnets has concentric curved inner and outer sides. 7. An electrical submersible well pump assembly, comprising: a rotary pump having a rotatable pump shaft;a motor having a motor shaft that is rotated by the motor and extends along an axis of the pump assembly;a magnetic coupling unit, comprising:an inner rotor operatively coupled to one of the pump or motor shafts for rotation therewith, the inner rotor having a plurality of slots therein, each of the slots having an outer wall spaced radially inward from an outer diameter surface of the inner rotor;a plurality of inner rotor magnets, each located within one of the slots;an outer rotor surrounding the inner rotor and operatively coupled to the other of the pump or motor shafts for rotation therewith;a plurality of outer rotor magnets mounted to the outer rotor to attract the magnetic fields of the inner rotor magnets and cause the inner and outer rotors to rotate in unison; wherein:the inner rotor comprises a plurality of inner rotor segments in axial abutment with each other, each of the segments comprising a plurality of steel discs stacked together, each of the discs having apertures that define the slots and a periphery that defines an outer diameter of each of the inner rotor segments;a plurality of non magnetic, electrically conductive damper bars in each of the inner rotor segments, each of the damper bars extending through holes provided in the discs at a location between the outer wall of one of the slots and the outer diameter of the inner rotor segment, the damper bars being spaced around and parallel to the axis; andend caps on opposite ends of each of the rotor segments, the damper bars extending to and being joined to each of the end caps. 8. An electrical submersible well pump assembly, comprising: a rotary pump having a rotatable pump shaft;a motor having a motor shaft that is rotated by the motor and extends along an axis of the pump assembly;an inner rotor having an inner rotor shaft operatively coupled to the motor shaft for rotation therewith, the inner rotor comprising a plurality of inner rotor segments, each of the segments comprising steel discs stacked together with end caps at each end of each of the inner rotor segments;the discs having apertures that align to define axially extending slots therein, the slots being spaced apart from each other around the inner rotor shaft, each of the slots having an inner wall and an outer wall, the inner wall being spaced radially outward from the inner rotor shaft, the outer wall being spaced radially inward from an outer diameter surface of the inner rotor;a plurality of inner rotor magnets located within the slots, the inner rotor magnets defining an inner rotor magnet array that extends from a pump end of the inner rotor to a motor end of the inner rotor;a plurality of damper bars extending axially along each of the inner rotor segments and spaced apart from each other around the inner rotor shaft, the damper bars being located between the outer walls of the slots and the outer diameter surface of the inner rotor, each of the damper bars being formed of an electrically conductive, non magnetic material and having ends connected to the end caps;an outer rotor having a bore that receives the inner rotor, the outer rotor being operatively coupled to the pump shaft for rotation therewith; anda plurality of outer rotor magnets mounted to the bore of outer rotor to interact with magnetic fields of the inner rotor magnets and cause the inner and outer rotors to rotate in unison. 9. The assembly according to claim 8, further comprising: a plurality of flux barrier cavities, each extending outward from a side edge of one of the slots toward but not completely to the outer diameter surface of the inner rotor. 10. The assembly according to claim 8, further comprising: an outer housing surrounding the outer rotor, the outer housing being non rotatable relative to the motor shaft and the pump shaft and having a motor adapter and a pump adapter;the outer rotor being separated from the outer housing by an annular outer gap;a non rotating inner rotor barrier surrounding the inner rotor, the inner rotor barrier having a cylindrical sidewall located between the outer rotor and the inner rotor, the inner rotor barrier being separated from the outer rotor by an annular intermediate gap, the inner rotor barrier begin separated from the inner rotor by an annular inner gap;the inner rotor barrier having a closed pump end and an open motor end configured for receiving lubricant from the motor through the motor adapter of the outer housing into the inner gap and into the inner rotor barrier;the intermediate and the outer gaps being configured to receive from the pump end of the outer housing well fluid in which the assembly is immersed;the inner gap and the intermediate gap having axial lengths at least equal to an axial length along the inner rotor of the inner magnet array; andthe inner gap and the intermediate gap being open and unobstructed for an axial length at least equal to an axial length of the inner magnet array. 11. The assembly according to claim 8, further comprising: an outer housing surrounding the outer rotor, the outer housing being non rotatable relative to the motor shaft and the pump shaft and having a motor adapter and a pump adapter;the outer rotor being located in and rotatable relative to the outer housing, the outer rotor being separated from the outer housing by an annular outer gap;an inner rotor barrier surrounding the inner rotor, the inner rotor barrier having a cylindrical sidewall located between the outer rotor and the inner rotor, the inner rotor barrier being separated from the outer rotor by an annular intermediate gap, the inner rotor barrier being separated from the inner rotor by an annular inner gap;the inner rotor barrier having a closed pump end and an open motor end configured for receiving lubricant from the motor through the motor adapter of the outer housing into the inner gap and into the inner rotor barrier;the intermediate and the outer gaps being configured to receive from the pump end of the outer housing well fluid in which the assembly is immersed;inner rotor radial support bearings at opposite ends of the inner rotor; whereinthe inner gap is continuous and open from one of the inner rotor radial support bearings to the other of the inner rotor radial support bearings;outer rotor radial support bearings at opposite ends of the outer rotor; andwherein the outer and the intermediate gaps are continuous and open from one of the outer rotor radial support bearings to the other of the outer rotor radial support bearings. 12. The assembly according to claim 8, wherein: each of the inner rotor magnets has an inner side and an outer side that are flat and parallel to each other. 13. The assembly according to claim 8, further comprising: a non conductive coating on opposite sides of each of the discs.