Motor with a disk rotor

Brushless d.c. motor comprising a multipolar permanent magnet rotor, stator means having a plurality of ironless coils arranged in a one-layer winding arrangement, said coils being connected to form a plurality of phase windings (122, S1-S4), rotor positions sensing means (76,77;

• 254,255;
• 254',255';
• 296,297) for controlling the currents in said phase windings so as to obtain four current pulses per rotor rotation angle of 360 electrical degrees and to create in operation a rotary magnetic field driving said permanent magnet rotor, said winding arrangement comprising at least one set of four coils, of which the first coil has a center distance of 270 electrical degrees from the second coil, the second coil has a center distance of 270 electrical degrees from the third coil, and the third coil has a center distance of 270 electrical degrees from the fourth coil, the first coil being electrically connected with the third coil and oppositely poled with respect to it, and the second coil being electrically connected with the fourth coil and being oppositely poled with respect to it.

Brushless d.c. motor having a substantially disk-shaped permanent magnet rotor mounted on a shaft, a flat air gap and an iron-free stator winding arrangement comprising four individual coils affixed to the motor casing at their radially outer portions so that said coils extend self-supportedly into said air gap, of which coils the first has a center-to-center spacing of 270 electrical degrees from the second, the second likewise from the third, and the third likewise from the fourth, said rotor comprising spacing means (93) located radially inward of said stator winding arrangement and between rotor portions extending respectively on both sides of said stator winding arrangement for withstanding magnetically produced axial forces between said rotor portions, said motor casing (12) being substantially shell-shaped and arranged to surround at least part of said rotor, said spacing means (93) surrounding with an interposed clearance a tubular bearing means (13) firmly attached to said motor casing (12) for journalling the shaft (11) of said rotor, said spacing means (93) being mounted so as to rotate with said shaft (11).

Low-speed brushless d.c. motor comprising a substantially disk-shaped permanent magnet rotor mounted on a shaft, magnetic return path means substantially parallel to the disk plane of said rotor defining a flat air gap between said rotor and said return path means, an iron-free stator winding predominantly located in said air gap and a tachogenerator coaxial with said shaft on the opposite side of said return path means from said rotor, said tachogenerator comprising a speed measuring coil (42) through which said shaft passes coaxially thereto, means for causing a magnetic flux varying at a rate dependent on the speed of the motor to be linked through said speed measuring coil for inducing an alternating voltage therein of a frequency dependent upon motor speed and

• a compensation coil (43) coaxial with said shaft and with said speed measuring coil mounted so as to be substantially uninfluenced by the flux of said magnetic flux which varies at a rate dependent on motor speed and so mounted as to be linked by the same stray flux as is linked through said speed measuring coil, said compensation coil being connected so as to superpose its output on the output of said speed measuring coil for reducing the effects of stray flux on the combined output.