Magnetic sensor for switched reluctance motor

A sensing apparatus for use on a polyphase switched reluctance motor having a stator assembly and a rotor assembly including a rotor shaft on which a rotor is mounted for rotation with respect to the stator, each respective motor phase being switched between active and inactive states under the control of a commutation means responsive to sensed motor operating conditions, switching a phase to its active state including supplying current to respective rotor phase windings, and switching the phase to its inactive state including cessation of the current supply whereby there is a turn-on, running, and turn-off portion of each cycle of current supply the phase the turn-on portion of the cycle lasting approximately 30%-45% the time period of the phase, the apparatus comprising sensing means for continuously sensing the position of the shaft and including a magnetic ring installed on the rotor shaft and rotatable therewith and a sensing means for sensing changes in a magnetic field produced by the ring as it rotates with the shaft, the magnet ring having a set of magnetic poles for each rotor pole with the portion of the circumference of the ring subtended by one of the poles of each set being a greater portion of the circumference than that subtended by the other pole of the set, the respective portions of the ring circumference subtended by the poles in each set being proportional to the turn-off time to the turn-on time with the larger pole segment subtending an arcuate segment equal to (0.70-0.55)(360/the number of rotor poles) and the smaller pole segment subtending an arcuate segment equal to (0.30-0.45)(360/the number of rotor poles), and the motor having N phases where N is a positive integer greater than one, and the sensing means including a plurality of sensors the number of which is a function of the number of motor phases and is constant integer value greater than zero, and with one sensor being used for two motor phases.

A method of controlling phase commutation in a polyphase switched reluctance motor having N phases where N is a positive whole integer greater than one, the motor having a stator assembly and a rotor assembly including a rotor shaft on which a rotor is mounted for rotation with respect to the stator, comprising:

• switching each respective motor phase being between an active and an inactive state under the control of a commutation means responsive to sensed motor operating conditions;
• continuously sensing the position of the shaft using a magnetic ring installed on the shaft and rotatable therewith, and a number of sensors, the number of said sensors being a function of the number of motor phases and with one sensor being used for two motor phases, each sensor sensing changes in a magnetic field produced by the ring as the ring rotates with the shaft and supplying signals indicative of rotor position to the commutation means and with one of the sensors, wherein switching a phase to the phase active state includes supplying current to the respective rotor phase windings, and switching the phase to the phase inactive state includes ceasing the current supply, there being a turn-on, running, and turn-off portion of each cycle of current supply to the phase, the turn-on portion of the cycle lasting approximately 30%-45% the period of the phase cycle;
• and,
• forming the magnetic ring to have a set of magnetic poles for each motor phase with the portion of the circumference of the ring subtended by one of the poles of each set being a greater portion of the circumference than that subtended by the other pole of the set, the respective portions of the circumference subtended by the poles in each set being proportional to the turn-off time to the turn-on time with the larger pole segment subtending an arcuate segment equal to (0.70-0.55)(360/the number of rotor poles) and the smaller pole segment subtending an arcuate segment equal to (0.30-0.45)(360/the number of rotor poles).