Coreless electric machine with magnet coils with effective coil part and end coil parts

1. A coreless electric machine comprising:

a rotor including a permanent magnet and rotating about a center axis; and

a stator with a coil assembly including a combination of 2N magnet coils where N is an integer of two or more, the stator being arranged concentrically with the rotor via a gap from the rotor, wherein

each of the magnet coils is configured as a concentrated winding coil including an effective coil part, a first coil end part and a second coil end part provided on opposite sides of the effective coil part, and an air core region surrounded by the effective coil part, the first coil end part, and the second coil end part,

the 2N magnet coils include N first shape coils each having a shape in which the first coil end part is bent inwardly from the effective coil part in a radial direction of the stator, and N second shape coils each having a shape in which the second coil end part is bent outwardly from the effective coil part in the radial direction,

outer side surfaces of the effective coil parts of adjacent ones of the first shape coils contact each other,

outer side surfaces of the effective coil parts of adjacent ones of the second shape coils contact each other,

the coil assembly has a structure in which (i) the effective coil part of the second shape coil is housed in the air core region of the first shape coil, and the effective coil part of the first shape coil is housed in the air core region of the second shape coil; and (ii) the first shape coils and the second shape coils are arranged alternately, one by one,

the outer shape of each of the magnet coils in a section perpendicular to the center axis is a divided ring-like shape defined by dividing a circular ring into equal N parts, and two sides of the divided ring-like shape form an angle set to be 360°/N or less,

a total length of the first coil end part and the second coil end part of each of the first shape coils along the center axis is greater than a total length of the first coil end part and the second coil end part of each of the second shape coils along the center axis, and

coil conductive wires for the first shape coil and the second shape coil have an equal length.

2. The coreless electric machine according to claim 1 , wherein

the length of the first coil end part of each of the first shape coils along the center axis is greater than the length of the second coil end part of each of the second shape coils along the center axis.

3. The coreless electric machine according to claim 1 , wherein

an array of the coil conductive wire in each of the magnet coils in a section perpendicular to the center axis includes multiple layers stacked in the radial direction, and the number of turns of the coil conductive wire in each of the multiple layers is set in such a manner that the number of turns of the coil conductive wire increases monotonously in a more external layer in the radial direction.

4. The coreless electric machine according to claim 1 , wherein

each of the magnet coils includes the coil conductive wire including a conductive wire bundle as a bundle of multiple non-insulated conductive wires each being a non-insulated wire, and an insulating coating layer covering periphery of the conductive wire bundle.

5. The coreless electric machine according to claim 4 , wherein

the conductive wire bundle is braided.

6. The coreless electric machine according to claim 4 , wherein

each of the non-insulated conductive wires is a non-plated copper wire.