초록 ▼

A universal motor (18) for a power tool (10) has a stator assembly (22) and an armature (24). The stator assembly includes a plurality of interconnected field windings (28-34) to which current is supplied to run the motor. The armature has a commutator (36) including brushes (40a, 40b) for circulati

A universal motor (18) for a power tool (10) has a stator assembly (22) and an armature (24). The stator assembly includes a plurality of interconnected field windings (28-34) to which current is supplied to run the motor. The armature has a commutator (36) including brushes (40a, 40b) for circulating current through the armature. To quickly and safely brake the motor, without excessively damaging the brushes, a switch (16) is interposed between an AC power source for the motor and the armature. In one embodiment, the switch shorts the armature during braking. In this embodiment, the switch includes sets (56, 58, 60) of electrical contacts by which the inner field windings (28, 30) are connected in series with the outer filed windings (32, 34); and the field windings are series connected with the armature. When the motor is braked, the switch is moved to a position opening the electrical connection between the power source and the outer field winding, while maintaining the electrical connection with the inner field windings. The switch includes electrical contacts across which the armature is connected when the motor is braked. The armature is shorted across these electrical contacts to help brake the motor.

대표청구항 ▼

In a universal motor having a stator assembly and an armature, the stator assembly having a central bore in which the armature is positioned for rotational movement relative to the stator assembly, and a plurality of interconnected field windings to which current is supplied to run the motor, the fi

In a universal motor having a stator assembly and an armature, the stator assembly having a central bore in which the armature is positioned for rotational movement relative to the stator assembly, and a plurality of interconnected field windings to which current is supplied to run the motor, the field windings including two inner field windings and two outer field windings, the armature including a commutator for circulating current through the armature and one outer field winding being series connected with the armature, the commutator including brushes contacting the armature for routing electrical current through the armature, the improvement comprising means for braking the motor to stop its rotation, said braking means including switch means interposed between an AC power source for the motor and the armature for switching electrical connections between the field windings to effect a braking action of the motor without causing an excessive commutator brush wear thereby to quickly and safely brake the motor without damaging the brushes, the switch means including a switch for changing the electrical interconnections between the respective windings when the motor is to be braked, the switch including sets of electrical contacts by which the inner field windings are series connected to the other outer field winding, and the inner field windings and other outer field winding are connected in series with the one outer field winding and the armature when the switch is in a motor running position, and the switch position, when the motor is braked, opening and electrical connection between a source of power to the inner field windings and said other outer field winding, and the switch including an additional set of electrical contacts across which the armature and the series connected one outer field winding are connected when the motor is braked, said additional set of electrical contacts shorting the armature and said one outer field winding thereby to stop the motor.