US3794898A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Dynamic braking of electric motors with thermistor braking circuit
Assignee: Individual
•
Filing: 1973-02-26
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Granted: 1974-02-26
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Expires: 1993-02-26
Abstract
Abstract A motor system for energizing and deenergizing an electric motor and for dynamically braking the motor to a halt after deenergization. When the motor is turned off, a dynamic braking circuit is connected in series with the motor windings to assure generator action and to provide for dissipation of the kinetic energy of the motor. The braking circuit incorporates a thermistor through which braking currents flow. Because of its comparatively high resistance at ambient temperatures the thermistor opposes high surge currents at the initiation of braking, thereby reducing arcing at the motor brushes when the kinetic energy of the motor is highest. As the motor decelerates, the resistance of the thermistor reduces automatically because of self-heating, thereby maintaining large currents in the braking circuit to bring the motor quickly to a halt.
Inventors
- 👤 T Gross
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 22:16
CPC Classifications
H; H02; H02P; H02P3/00; H02P3/06; H02P3/18; H02P3/22
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
99 words
A dynamically braked motor system comprising: an electric motor operable both in a motor mode and in a generator mode; supply terminals connectable to a source of electrical power; switching means for controlling the connection of said motor to said supply terminals; means made operative upon disconnection of said motor from said supply terminals for completing a dynamic braking circuit with said motor, said dynamic braking circuit including at least one thermistor self-heated by currents in said braking circuit to reduce the value of the resistance in said braking circuit in response to the dissipation of braking energy therein.
Claim 2
Dependent Claim
99 words
A dynamically braked motor system comprising: an electric motor operable both in a motor mode and in a generator mode; supply terminals connectable to a source of electrical power; switching means for controlling the connection of said motor to said supply terminals; means made operative upon disconnection of said motor from said supply terminals for completing a dynamic braking circuit with said motor, said dynamic braking circuit including at least one thermistor self-heated by currents in said braking circuit to reduce the value of the resistance in said braking circuit in response to the dissipation of braking energy therein.
Claim 3
Dependent Claim
135 words
A control system for energizing and for dynamically braking an electric motor operable both in a motor mode and in a generator mode comprising: supply terminals connectable to a source of electrical power; switching means for controlling the connection of such a motor to said supply terminals; current-limiting means including at least one thermistor having a negative temperature coefficient of resistance such that said current limiting means exhibits a Declining resistance characteristic in response to the flow of self-heating currents therein; and means made operative upon disconnection of such electric motor from said supply terminals for completing a dynamic-braking circuit with such motor through said current-limiting means, whereby the value of the resistance in said braking circuit is automatically reduced from an initial value to lower values during the operative period of said braking circuit.
Claim 4
Dependent Claim
135 words
A control system for energizing and for dynamically braking an electric motor operable both in a motor mode and in a generator mode comprising: supply terminals connectable to a source of electrical power; switching means for controlling the connection of such a motor to said supply terminals; current-limiting means including at least one thermistor having a negative temperature coefficient of resistance such that said current limiting means exhibits a Declining resistance characteristic in response to the flow of self-heating currents therein; and means made operative upon disconnection of such electric motor from said supply terminals for completing a dynamic-braking circuit with such motor through said current-limiting means, whereby the value of the resistance in said braking circuit is automatically reduced from an initial value to lower values during the operative period of said braking circuit.
Claim 5
Independent Claim
26 words
The system of calim 2 wherein said current-limiting means includes at least one additional discrete resistor connected in series with said thermistor in said braking circuit.
Claim 6
Independent Claim
26 words
The system of calim 2 wherein said current-limiting means includes at least one additional discrete resistor connected in series with said thermistor in said braking circuit.
Claim 7
Dependent Claim
26 words
The system of claim 2 wherein said current-limiting means includes at least one further discrete resistor connected in shunt with said thermistor in said braking circuit.
Claim 8
Dependent Claim
33 words
The system of claim 4 wherein a thermal bond is provided between said further discrete resistor and said thermistor to cause heating of said thermistor by braking currents in said further discrete resistor.
Claim 9
Dependent Claim
18 words
The system of claim 2 wherein means are provided for cooling said thermistor subsequent to said braking interval.
Claim 10
Dependent Claim
43 words
The system of claim 2 wherein said current-limiting means is a resistive network including at least one additional discrete resistor connected in series with said thermistor and at least one further discrete resistor connected in parallel with said thermistor in said braking circuit.
Claim 11
Dependent Claim
117 words
A control system for energizing and for dynamically braking an electric motor which is capable of generating electric currents, said system comprising: supply terminals connectable to a source of currents; switching means for controlling the connection of such a motor to said supply terminals; current-limiting impedance means; means made operative upon disconnection of such motor from said supply terminals for completing a dynamic-braking circuit through such motor and said impedance means; and load-reducing means comprising a thermistor self-heated by currents in said braking circuit and responsive to the dissipation of a predetermined quantity of energy by said braking circuit for reducing the value of the impedance in said braking circuit, thereby to reduce the total braking interval.
Claim 12
Dependent Claim
117 words
A control system for energizing and for dynamically braking an electric motor which is capable of generating electric currents, said system comprising: supply terminals connectable to a source of currents; switching means for controlling the connection of such a motor to said supply terminals; current-limiting impedance means; means made operative upon disconnection of such motor from said supply terminals for completing a dynamic-braking circuit through such motor and said impedance means; and load-reducing means comprising a thermistor self-heated by currents in said braking circuit and responsive to the dissipation of a predetermined quantity of energy by said braking circuit for reducing the value of the impedance in said braking circuit, thereby to reduce the total braking interval.
Claim 13
Dependent Claim
112 words
A control system for energizing and for dynamically braking an electric motor which is capable of generating electric currents, said system comprising: supply terminals connectable to a source of electrical power; switching means for controlling the connection of such motor to said supply terminals; means made operative upon disconnection of such motor from said supply terminals for completing a dynamic-braking circuit through such motor, said dynamic braking circuit including at least one thermistor self-heated by currents in said braking circuit for presenting a higher resistance to said currents upon the initiation of braking and thereafter a reduced level of said resistance in response to the dissipation of energy by said braking circuit.
Claim 14
Dependent Claim
112 words
A control system for energizing and for dynamically braking an electric motor which is capable of generating electric currents, said system comprising: supply terminals connectable to a source of electrical power; switching means for controlling the connection of such motor to said supply terminals; means made operative upon disconnection of such motor from said supply terminals for completing a dynamic-braking circuit through such motor, said dynamic braking circuit including at least one thermistor self-heated by currents in said braking circuit for presenting a higher resistance to said currents upon the initiation of braking and thereafter a reduced level of said resistance in response to the dissipation of energy by said braking circuit.
Claim 15
Dependent Claim
33 words
The system of claim 9 wherein said dynamic braking circuit comprises a resistive network of which said thermistor is a part, said network including a shunt resistor connected in parallel with said thermistor.
Claim 16
Dependent Claim
33 words
The system of claim 9 wherein said dynamic braking circuit comprises a resistive network of which said thermistor is a part, said network including a series resistor connected in series with said thermistor.
Claim 17
Dependent Claim
117 words
The system of claim 9 wherein said dynamic braking circuit comprises a resistive network of which said thermistor is a part, said network including a series resistance in series with said thermistor to dissipate an increased share of braking energy when said thermistor is at elevated temperatures, and a shunt resistance in parallel with said thermistor to reduce the resistance of said network at low temperatures; said system further comprising a thermal bond between said shunt resistance and said thermistor to warm said thermistor at especially low Temperatures by virtue of braking currents in said shunt resistance, and means for cooling said thermistor subsequent to the braking interval to restore said system rapidly to a pre-braking condition.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-02-25 | 1977-08-27 | 1978-02-26 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-02-25 | 1981-08-27 | 1982-02-26 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-02-25 | 1985-08-27 | 1986-02-26 | $7700.00 | Window Closed / Lapsed |