A New Variable Speed Permanent Magnet D-C Motor

This paper discusses a new high efficiency variable speed permanent magnet (PM) d-c electric motor designed for initial use in windshield wiper assemblies on 1967 passenger cars. It traces the development from the basic two-speed, three-brush PM motor to the more sophisticated variable speed unit.

Laboratory test data are used to compare performance of a variable speed wire-wound design and a two-speed PM motor with the new variable speed PM unit. Evolution of the needed circuitry is discussed and illustrated. The importance of using a diode in the circuit is stressed as the key to success in the high efficiency variable speed PM development.