This invention relates to a motor control system for a brushless DC motor having an inverter responsively coupled to the motor control system and in power transmitting relationship to the motor. The motor control system includes a motor rotor speed detecting unit that provides a pulsed waveform signal...http://www.google.ca/patents/US4546293?utm_source=gb-gplus-sharePatent US4546293 - Motor control for a brushless DC motor
