RESISTANCE COMPENSATION IN A MOTOR USING A THERMALLY VARIABLE RESISTIVE NETWORK

A motor is disclosed comprising a housing (5) and a plurality of parallel stator laminations (4) mounted on the interior wall of the housing surrounding the rotor (3). The stator (4) comprises a plurality of coils (28) wound around the stator poles (26). Each coil or group of coils connected in series with each other are further connected in series with a thermistor network (29). Preferably, the thermistor (30) is supported on a printed circuit board (36) mounted adjacent to the coils (28), with the thermistor (30) being inserted in a space directly adjacent to or between adjacent stator coils (28) in order for the thermistor (30) to accurately respond to the actual operating temperature of the coils (28). With increases in temperature, the resistance of the negative temperature coefficient thermistor (30) will decrease, lowering the resistance of the motor circuit and maintaining the L/R time constant of the system. The opposite effect will occur with decreasing temperature. To adjust for the fact that thermistors that accurately reflect the changes in resistance of the wire used to wind the coils (28) with changes in temperature are not available, a resistor (32) is wired in parallel with the thermistor (30), the resistor (32) having a value chosen to modify the total resistance represented by the thermistor network (29) to the coils (28) so that the compensation is accurate over a wide range of changes in temperature and motor design. The shunt resistor (32) allows flexibility in motor design, as it can have any selected value from zero to infinity to compensate for variations in motor design. Le moteur décrit comprend un logement (5) et plusieurs strates de stator parallèles (4) montées sur la paroi intérieure du logement entourant le rotor (3). Le stator (4) comprend plusieurs enroulements (28) enroulés autour des pôles (26) du stator. Chaque enroulement ou groupe d'enroulements connectés en série entre eux sont en outre connectés en série à un réseau de thermistors (29). Le thermistor (30) est de préférence placé sur une carte de circuits imprimés (36) montée adjacente aux enroulements (28), le thermistor (30) étant inséré dans un espace directement adjacent aux enroulements (28) du stator ou entre des enroulements adjacents (28) du stator, de façon à permettre au thermistor (30) de réagir avec précision à la température d'activation effective des enroulements (28). Lors d'accroissements de température, la résistance du thermistor à coefficient de te