Small diameter brushless direct current linear motor and method of using same

A method of using a linear motor for driving reciprocatively a downhole pump, comprising:

• securing removably together a plurality of large circular iron lamination sections and a plurality of small circular iron lamination sections for defining stator core having a plurality of spaced apart transversely disposed coil receiving slots and an axially extending bore;
• mounting within each one of said slots an annularly shaped coil;
• energizing said coils with rectangular pulses of electrical current for producing a series of electromagnetic fields extending at least partially in an axial direction;
• mounting an elongated member telescopically within said bore;
• mounting a plurality of annularly-shaped permanent magnets on said elongated member in an axially spaced apart manner to generate a series of magnetic fields extending at least partially in an axial direction opposed to the fields produced by the individual ones of said coils when individual ones of said magnets are in opposition to corresponding individual ones of said coils to urge said rod to produce relative movement along a path of travel defined by said bore;
• and
• mounting a plurality of thin annularly-shaped spacer disposed on said elongated member interleaved with said magnets to shunt a portion of said magnetic fields produced by said magnets to reduce substantially core flux losses on said stator core.

A system for pumping fluids through a production tube from a downhole well to the ground surface, comprising:

• a motor-pump cartridge unit having a pump for pumping the well fluids to the ground surface and a linear motor for driving said pump reciprocatively;
• said linear motor including a stator assembly and a mover assembly;
• said stator assembly including annular core means defining a plurality of spaced apart coil receiving slots, and coil means for producing a series of electromagnetic fields extending at least partially in an axial direction when energized with an electrical current by said motor controller means;
• said coil means including a plurality of individual annular-shaped coils disposed individually within said slots;
• said mover assembly including an elongated member mounted telescopically reciprocatively within said core means;
• a plurality of annularly-shaped permanent magnets mounted on said member in an axially spaced apart manner for generating magnetic fields extending at least partially in an axial direction opposed to the fields produced by said coil means when individual ones of said magnets are disposed in opposition to corresponding individual ones of said coils to urge said mover assembly to produce relative movement between said stator and said mover;
• and a plurality of thin annularly-shaped spacers mounted on said member for shunting a portion of said magnetic fields produced by said magnets to reduce substantially core flux losses in said core means;
• and
• housing means coupled to said stator assembly for defining a given path of travel for said mover assembly;
• said housing means and said stator assembly having a very small transverse thickness to axial length ratio to enable said motor-pump cartridge unit to be received within the production tube for mounting purposes.