Motor end cap with interference fit
A rotary machine (e.g., motor or generator) has end caps with plastic piloting rings that engage a stator's plastic winding frame in an interference fit, so that a rotor seated by bearings in the end caps is properly aligned with the stator. The flexibility of the plastic-to-plastic fit allows looser tolerances in comparison to machining of all-metal end caps, while the average circle of the piloting ring's outer diameter still assures proper concentricity of rotor shaft, bearings, piloting rings and stator.
1. A rotary machine, comprising:
a stator including a plastic winding frame with an inner diameter that is honed at each end to be in-line with a stator inner diameter, such that the frame inner diameter can serve to pilot the positioning of a rotor within the stator; and
a first end cap having a plastic piloting ring with an inner diameter seating a first bearing and with an outer diameter concentric with the inner diameter, the outer diameter of the piloting ring engaging the inner diameter of the plastic winding frame at a first end in a plastic-to-plastic interference fit such that the first bearing is concentric with the stator inner diameter;
a second end cap having a plastic second piloting ring with an inner diameter of the second end cap seating a second bearing and with an outer diameter of the second end cap concentric with the inner diameter of the second end cap, the outer diameter of the second piloting ring engaging the inner diameter of the plastic winding frame at a second end in a plastic-to-plastic interference fit such that the second bearing is concentric with the stator inner diameter; and
the rotor located within the stator between the first and second end caps, the rotor having an axial shaft seated by the first and second bearings concentric with the stator inner diameter such that the rotor is centered and aligned with the stator by the first and second end caps.
2. A rotary machine as in claim 1 , wherein at least one of the end caps is a metal plate with a central opening into which the plastic piloting ring has been molded in place.
3. A rotary machine as in claim 1 , wherein at least one of the end caps with piloting ring is a single piece of molded plastic.
4. A rotary machine as in claim 1 , wherein the first and second bearings are molded with the plastic piloting rings of the respective first and second end caps.
5. A rotary machine as in claim 1 , wherein each end cap is laser welded in place to a stator casing.
6. A rotary machine as in claim 1 , wherein at least one end cap is held in place with an adhesive composition.
7. A rotary machine, comprising:
a stator including a plastic winding frame with an inner diameter that is honed at each end to be in-line with a stator inner diameter, such that the frame inner diameter can serve to pilot the positioning of a rotor within the stator; and
a first end cap having a plastic piloting ring with an inner diameter seating a first bearing and with an outer diameter concentric with the inner diameter, the outer diameter of the piloting ring engaging the inner diameter of the plastic winding frame at a first end in a plastic-to-plastic interference fit such that the first bearing is concentric with the stator inner diameter;
a second end cap having a plastic second piloting ring with an inner diameter of the second end cap seating a second bearing and with an outer diameter of the second end cap concentric with the inner diameter of the second end cap, the outer diameter of the second piloting ring engaging the inner diameter of the plastic winding frame at a second end in a plastic-to-plastic interference fit such that the second bearing is concentric with the stator inner diameter; and
the rotor located within the stator between the first and second end caps, the rotor having an axial shaft seated by the first and second bearings concentric with the stator inner diameter such that the rotor is centered and aligned with the stator by the first and second end caps;
wherein the outer diameter of each piloting ring has a tolerance held at ±50 μm with an average circle matching that of honed ends of the plastic winding frame of the stator.
8. A rotary machine, comprising:
a stator including a plastic winding frame with an inner diameter that is honed at each end to be in-line with a stator inner diameter, such that the frame inner diameter can serve to pilot the positioning of a rotor within the stator; and
a first end cap having a elastic piloting ring with an inner diameter seating a first bearing and with an outer diameter concentric with the inner diameter, the outer diameter of the piloting ring engaging the inner diameter of the plastic winding frame at a first end in a plastic-to-plastic interference fit such that the first bearing is concentric with the stator inner diameter;
a second end cap having a plastic second piloting ring with an inner diameter of the second end cap seating a second bearing and with an outer diameter of the second end cap concentric with the inner diameter of the second end cap, the outer diameter of the second piloting ring engaging the inner diameter of the plastic winding frame at a second end in a plastic-to-plastic interference fit such that the second bearing is concentric with the stator inner diameter; and
the rotor located within the stator between the first and second end caps, the rotor having an axial shaft seated by the first and second bearings concentric with the stator inner diameter such that the rotor is centered and aligned with the stator by the first and second end caps;
wherein the outer diameter of each piloting ring has a run-out held at ±75 μm relative to the corresponding inner diameter of the same piloting ring.
9. A method of assembling a rotary machine, comprising:
providing a stator including a plastic winding frame with an inner diameter that is honed at each end to be in-line with a stator inner diameter;
attaching a first end cap to the stator, the first end cap including a plastic second piloting ring with concentric inner and outer diameters, the inner diameter of the second piloting ring seating a first bearing and the outer diameter of the second piloting ring engaging the inner diameter of the plastic winding frame at a first end in a plastic-to-plastic interference fit such that the first bearing is concentric with the stator inner diameter;
inserting a rotor into the stator with an axial shaft of the rotor seated in the first bearing; and
attaching a second end cap to the stator, the second end cap including a plastic piloting ring with concentric inner and outer diameters, the inner diameter of the piloting ring seating a second bearing and the outer diameter of the piloting ring engaging the inner diameter of the plastic winding frame at a second end in a plastic-to-plastic interference fit such that the second bearing is concentric with the stator inner diameter, the second bearing seating the axial shaft of the rotor such that the axial shaft is concentric with the stator inner diameter and the rotor is thereby centered and aligned within the stator.
10. A method as in claim 9 , wherein at least one of the end caps is formed by molding a plastic piloting ring within a central opening of a metal plate.
11. A method as in claim 9 , wherein at least one of the end caps is formed with its piloting ring as a single piece of molded plastic.
12. A method as in claim 9 , wherein the first and second bearings are molded with the plastic piloting rings of the respective first and second end caps.
13. A method as in claim 9 , further defined by laser welding each end cap in place to a stator casing.
14. A method as in claim 9 , further defined by adhering at least one end cap in place.
15. A method of assembling a rotary machine, comprising:
providing a stator including a plastic winding frame with an inner diameter that is honed at each end to be in-line with a stator inner diameter;
attaching a first end cap to the stator, the first end cap including a plastic second piloting ring with concentric inner and outer diameters, the inner diameter of the second piloting ring seating a first bearing and the outer diameter of the second piloting ring engaging the inner diameter of the plastic winding frame at a first end in a plastic-to-plastic interference fit such that the first bearing is concentric with the stator inner diameter;
inserting a rotor into the stator with an axial shaft of the rotor seated in the first bearing; and
attaching a second end cap to the stator, the second end cap including a plastic second piloting ring with concentric inner and outer diameters, the inner diameter of the second piloting ring seating a second bearing and the outer diameter of the second piloting ring engaging the inner diameter of the plastic winding frame at a second end in a plastic-to-plastic interference fit such that the second bearing is concentric with the stator inner diameter, the second bearing seating the axial shaft of the rotor such that the axial shaft is concentric with the stator inner diameter and the rotor is thereby centered and aligned within the stator;
wherein the outer diameter of each piloting ring is formed to a tolerance held at ±50 μm with an average circle matching that of honed ends of the plastic winding frame of the stator.
16. A method of assembling a rotary machine, comprising:
providing a stator including a plastic winding frame with an inner diameter that is honed at each end to be in-line with a stator inner diameter;
attaching a first end cap to the stator, the first end cap including a plastic second piloting ring with concentric inner and outer diameters, the inner diameter of the second piloting ring seating a first bearing and the outer diameter of the second piloting ring engaging the inner diameter of the plastic winding frame at a first end in a plastic-to-plastic interference fit such that the first bearing is concentric with the stator inner diameter;
inserting a rotor into the stator with an axial shaft of the rotor seated in the first bearing; and
attaching a second end cap to the stator, the second end cap including a plastic second piloting ring with concentric inner and outer diameters, the inner diameter of the second piloting ring seating a second bearing and the outer diameter of the second piloting ring engaging the inner diameter of the plastic winding frame at a second end in a plastic-to-plastic interference fit such that the second bearing is concentric with the stator inner diameter, the second bearing seating the axial shaft of the rotor such that the axial shaft is concentric with the stator inner diameter and the rotor is thereby centered and aligned within the stator;
wherein the outer diameter of each piloting ring is formed with a run-out held at ±75 μm relative to the corresponding inner diameter of the same piloting ring.