Patent ID: 8421380

Claim:
A direct current motor comprising a stator and a rotor, the rotor comprising: a shaft; a rotor core fixed to the shaft; a commutator fixed to the shaft; rotor windings wound about poles of the rotor core and terminated on the commutator; a common brush and at least two selectable brushes in sliding contact with the commutator; at least two direct current power sources; and a switching device configured to connect the common brush and a selected one of the selectable brushes with predetermined combinations of the power sources to operate the motor in different speed modes; wherein the at least two selectable brushes comprises a low speed brush corresponding to low speed operation of the motor and a high speed brush corresponding to high speed operation of the motor; the switching device connects the power sources in series between the common brush and the high speed brush, to operate the motor in a high speed mode; the switching device connects the power sources in parallel between the common brush and the low speed brush, to operate the motor in a low speed mode; the at least two direct current power sources comprises a first power source and a second power source, and the switching device comprises three single pole double throw switches and each switch comprises two contact points and one contact arm; the first switch has one contact point connected with the positive terminal of the first power source and the fixed end of the contact arm connected with the positive terminal of the second power source; the second switch has one contact point connected with the positive terminal of the first power source, the other contact point connected with the negative terminal of the first power source and the common brush, and the fixed end of the contact arm connected with the negative terminal of the second power source; and the third switch has one contact point connected to the low speed brush, the other contact point connected to the high speed brush, and the fixed end of the contact arm connected with the positive terminal of the second power source.