Towmotor Corporation

Caterpillar Tractor Co.

Ward L Bivens

Richard A Schwehr

Kenneth A Baumgartner

Frank S Buchwald

A delayed turn-on and turn-off control circuit for an electric motor includes a motor relay having an electrical actuator and a normally open motor contactor which is connected in series between the motor and an electrical power source for running the motor when the electrical actuator is energized. A normally non-conductive electrical switching device is serially connected between the electrical actuator and the power source. A turn-on delay circuit is responsive to closing of a normally open motor start switch and produces an electrical signal to render the electrical switching device conductive only after a predetermined lapse of time following the closing of the motor start switch, thereby energizing the motor. A turn-off delay circuit is responsive to opening of the motor start switch and produces an electrical signal to render the electrical switching device nonconductive only after a predetermined lapse of time following the opening of the motor start switch, thereby causing the motor to be deenergized.

Delayed turn-on and turn-off control circuit

A DC electrical motor of the form having one field winding connected in series with the armature winding in addition to a shunt field winding connected in parallel with the armature winding is provided with a diode or the like in the shunt field winding circuit. This blocks reversed current flow in the shunt field winding which can otherwise occur during start-up due to an inductive interaction with the series field winding and armature circuit. The diode or the like enables faster magnetization of the stator poles by preventing creation of negative shunt field ampere turns due to the magnetic couple with the series field-armature circuit during the motor start period. Faster starting of the motor results, and adverse effects such as heating, brush deterioration, and commutation problems are reduced.

Compound D.C. electrical motor with shunt field demagnetization

A brush which presses against the commutator of a direct current machine has a groove in one side thereof into which a fixed probe partially extends. As the brush wears, movement thereof causes physical engagement of the probe with the end of the groove to complete a current path through the probe. Flow through the current path energizes and latches a warning device.

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Painesville, OH, United States of America

Ward L Bivens