Electrothermal motor starting apparatus

Claim 2

Apparatus for automatically deenergizing the start winding of an electric motor after a predetermined delay following energization of said motor, said apparatus comprising: thermally responsive current switching means for controlling the flow of current to said start winding, said switching means including a temperature sensitive element which operates to deenergize said start winding when the temperature of said element exceeds a predetermined threshold; a PTC thermistor thermally coupled to said element for applying heat thereto for operating said switching means, said thermistor having a transition temperature above which the resistance of said thermistor rises relatively abruptlY, said transition temperature being above said threshold temperature; and means for electrically energizing said thermistor concurrently with the energization of said motor thereby to self-heat said thermistor which, after a predetermined delay of said temperature sensitive element to reach said threshold temperature, operates said switching means to deenergize said start winding and then maintains said switching means in its operated state substantially independent from variations in supply voltage and ambient temperature, further self-heating of said thermistor being limited by the increase of the resistance of said thermistor at said transition temperature.

Claim 3

Apparatus as set forth in claim 1 wherein said switching means includes a snap-acting thermostatic switch.

Claim 4

Apparatus as set forth in claim 1 wherein said PTC thermistor is connected across said start winding.

Claim 5

Apparatus for automatically deenergizing the start winding of an electric motor after a predetermined delay following energization of said motor, said apparatus comprising: thermally responsive current switching means for controlling the flow of current to said start winding, said switching means including a temperature sensitive element which operates to deenergize said start winding when the temperature of said element exceeds a predetermined threshold; a PTC thermistor thermally coupled to said element for applying heat thereto for operating said switching means, said thermistor having a transition temperature above which the resistance of said thermistor rises relatively abruptly, said transition temperature being above said threshold temperature; and means for connecting said thermistor in a circuit across said start winding to energize said thermistor concurrently with the energization of said start winding thereby to self-heat said thermistor which, after a predetermined delay for said temperature sensitive element to reach said threshold temperature, operates said switching means and deenergizes said start winding, said thermistor being maintained above said threshold temperature after deenergization of said start winding by the voltage induced in said winding by operation of said motor with further self-heating of said thermistor being limited by the increase of the resistance of said thermistor at said transition temperature independently of variations in said induced voltages.

Claim 6

Apparatus for automatically deenergizing the start winding of an electric motor after a predetermined delay following energization of said motor, said apparatus comprising: thermally responsive current switching means for controlling the flow of current to said start winding, said switching means including a temperature sensitive element which operates to deenergize said start winding when the temperature of said element exceeds a predetermined threshold; a PTC thermistor thermally coupled to said element for applying heat thereto for operating said switching means, said thermistor having a transition temperature above which the resistance of said thermistor rises relatively abruptly, said transition temperature being above said threshold temperature; and means for connecting said thermistor in a circuit across said start winding to energize said thermistor concurrently with the energization of said start winding thereby to self-heat said thermistor which, after a predetermined delay for said temperature sensitive element to reach said threshold temperature, operates said switching means and deenergizes said start winding, said thermistor being maintained above said threshold temperature after deenergization of said start winding by the voltage induced in said winding by operation of said motor with further self-heating of said thermistor being limited by the increase of the resistance of said thermistor at said transition temperature independently of variations in said induced voltages.

Claim 7

Apparatus for automatically deenergizing the start winding of an electric motor after a predetermined delay following energization of said motor, said apparatus comprising: a semiconductor current switching device which, when energized, applies current to said start winding; a triggering circuit, including a first thermistor, for controlling the energization of said semiconductor switching device, said triggering circuit being operative to energize said device except when the temperature of said first thermistor exceeds a predetermined threshold; a second thermistor thermally coupled to said first thermistor for applying heat thereto; and means for energizing said second thermistor concurrently with the energization of said motor thereby to self-heat said second thermistor which, after a predetermined delay for said first thermistor to reach said threshold temperature, causes said first thermistor to deenergize said switching device thereby deenergizing said start winding.

Claim 8

Apparatus for automatically deenergizing the start winding of an electric motor after a predetermined delay following energization of said motor, said apparatus comprising: a semiconductor current switching device which, when energized, applies current to said start winding; a triggering circuit, including a first thermistor, for controlling the energization of said semiconductor switching device, said triggering circuit being operative to energize said device except when the temperature of said first thermistor exceeds a predetermined threshold; a second thermistor thermally coupled to said first thermistor for applying heat thereto; and means for energizing said second thermistor concurrently with the energization of said motor thereby to self-heat said second thermistor which, after a predetermined delay for said first thermistor to reach said threshold temperature, causes said first thermistor to deenergize said switching device thereby deenergizing said start winding.

Claim 9

Apparatus as set forth in claim 5 wherein said semiconductor current switching device is a triac.

Claim 10

Apparatus as set forth in claim 5 wherein said triggering circuit includes a resistor connected in series with said first thermistor, and wherein said semiconductor switching device has a gate terminal which controls conduction through said device, said terminal being connected to a junction in said triggering circuit between said first thermistor and said resistor.

Claim 11

Apparatus as set forth in claim 5 wherein said means for energizing said second thermistor comprises cIrcuit means for connecting said thermistor in a circuit across said start winding whereby said thermistor is energized concurrently with said start winding and is maintained above said threshold temperature after deenergization of said start winding by the voltage induced in said start winding by operation of said motor.

Claim 12

Apparatus for automatically deenergizing the start winding of an electric motor after a predetermined delay following energization of said motor, said apparatus comprising: thermally responsive current switching means including a semiconductor current switching device for controlling the flow of current to said start winding, said switching means including a temperature sensitive element comprising a heat responsive thermistor for controlling conduction through said semiconductor device to deenergize said start winding when the temperature of said heat responsive thermistor exceeds a predetermined threshold; a PTC thermistor thermally coupled to said heat responsive thermistor, said PTC thermistor having a transition temperature above which the resistance of said PTC thermistor rises relatively abruptly, said transition temperature being above said threshold temperature; and means for electrically energizing said PTC thermistor concurrently with the energization of said motor thereby to self-heat said PTC thermistor which, after a predetermined delay of said heat responsive thermistor to reach said threshold temperature, operates said switching means to deenergize said start winding and then maintains said switching means in its operated state, further self-heating of said PTC thermistor being limited by the increase of the resistance of said PTC thermistor at said transition temperature.

Claim 13

Apparatus for automatically deenergizing the start winding of an electric motor after a predetermined delay following energization of said motor, said apparatus comprising: thermally responsive current switching means including a semiconductor current switching device for controlling the flow of current to said start winding, said switching means including a temperature sensitive element comprising a heat responsive thermistor for controlling conduction through said semiconductor device to deenergize said start winding when the temperature of said heat responsive thermistor exceeds a predetermined threshold; a PTC thermistor thermally coupled to said heat responsive thermistor, said PTC thermistor having a transition temperature above which the resistance of said PTC thermistor rises relatively abruptly, said transition temperature being above said threshold temperature; and means for electrically energizing said PTC thermistor concurrently with the energization of said motor thereby to self-heat said PTC thermistor which, after a predetermined delay of said heat responsive thermistor to reach said threshold temperature, operates said switching means to deenergize said start winding and then maintains said switching means in its operated state, further self-heating of said PTC thermistor being limited by the increase of the resistance of said PTC thermistor at said transition temperature.