Abstract: A wear-indicating brush and warning circuit is adapted to convey an indication that a dynamoelectric machine is in need of maintenance before the brush wears to the point that a rotor contact surface is damaged by contact with electrical connections to the brush. A brush (10) having current carrying pigtail leads (16) embedded therein includes a wear-detecting wire (20) embedded in the brush a short distance (A) beyond the lowest extent of the pigtail leads (16). The wire (20) is insulated over its periphery, including its tip (24), the insulation (26) being abraded by contact with the rotor contact surface (50), so that the wire (20) senses the voltage present thereon. Non-latching warning circuits (66, 66a), with and without the use of an isolating resistor within the dynamoelectric machine to permit the use of a single wire between the machine and the warning circuit to provide a brush wear indication.

Abstract: A permanent magnet motor is provided which has first and second U-shaped sections comprising the motor stator. Each section is constructed of low reluctance magnetic material. The motor armature shaft passes through a hole in the bight of each section and carries a commutator. An air space separates the bight and shaft to provide a high reluctance path to the shaft. The two parallel sides of the first section fit between the two sides of the second section in a contact relation; the combination defining a two piece magnetic circuit that passes around the motor from end to end. The first section contains a permanent magnet mounted upon each of the sides at diametrically opposite locations adjacent the armature. The flux coupling the two magnets passes through the armature core. The magnets define a pole pair and are spaced very close to the edge of the armature core to minimize the air gap between the armature and the magnet.