Patent ID: 8564231

Claim:
A method of sensing the direction of rotation in an electronically commutated motor (ECM) having a stator with a plurality of phases ( 24 , 26 ) and a permanent-magnet rotor ( 22 ), which rotor ( 22 ), during its rotation, induces voltages in the motor winding phases ( 24 , 26 ) of the stator, comprising the steps of: a) commutating the motor at a first time point, and at a second time point subsequent to said first time point, a time interval between said first and second time points defining a commutation period; b) sampling, at a plurality of characteristic points during said commutation period, either the profile of induced voltage in a presently currentless motor winding phase or the profile of a voltage drop at a transistor through which current is flowing to a presently energized motor winding phase, and storing measured values thereof; and c) deriving, from the measured values, rotor rotation direction; wherein there exists a predetermined time span (Tp) between two zero transitions of the induced voltage occurring in a currentless phase, or between two zero transitions of the voltage drop at the transistor through which current is flowing to the presently energized phase; and sampling is performed, to store a first measured value, at a time interval after a zero transition that is equal to approximately 20 to 30% of that predetermined time span (Tp).