COMMUTATORS

摘要

A commutator for an electric motor-generator comprises two opposed commutator elements (3, 4) each providing a continuous circumferential conducting surface (5, 6), to which a DC supply is connected via supply brushes (18, 19). A conductive commutation segment (7, 8) projects axially from each commutator element (3, 4). Three winding brushes (20, 21, 22) are located (120) degrees apart about the commutator. Each brush (20, 21, 22) engages alternately with the commutation segments (7, 8) and freewheeling segments (9, 10) as the commutator rotates. As each brush (20, 21, 22) moves from a commutation segment (7, 8) to a freewheeling segment (9, 10), the presence of the commutation ring (23) connecting the two freewheeling segments serves to inhibit sparking between the brush (20, 21, 22) and the commutation segment (7, 8). Alternatively, a plurality of brushes are provided for each phase, such that the winding current passing through each brush is reduced, thereby to reduce resistive losses.