Brushed direct current electric motor with salient pole rotor

1. A brush direct current motor, comprising:

a stator comprising a plurality of teeth and a plurality of coils wound around the teeth and corresponding to N phases;

a rotor coupling the stator, the rotor comprising a shaft, a rotor core fixed to the shaft and P salient poles made of magnetically conductive material and protruding from the shaft toward the teeth;

a first brush;

N second brushes; and

a commutator fixed to the shaft;

wherein the commutator comprises a first conductive ring, P first bars extending from the first conductive ring;

wherein the first brush is arranged to be electrically connected to a first terminal of a direct current power source and is arranged to make continuous sliding electrical contact with the first conductive ring, and the second brushes are arranged to make sliding electrical contact with the first bars; and

wherein one end of each phase is respectively connected to one of the N second brushes, and the other ends of each phase are arranged to be electrically connected to a second terminal of the direct current power source,

wherein the sum of the central angle “A” corresponding to the first bar and the central angle “B” corresponding to the second brush is not less than the commutation angle “β”, where β=|360/T−360/M|, “T” represents the number of stator teeth, and “M” represents the number of rotor poles.

2. The motor of claim 1 , wherein the stator has 6 coils and 6 teeth, and the rotor has 4 poles.

3. The motor of claim 1 , wherein the stator has 8 coils and 8 teeth, the rotor comprises 6 poles.

4. The motor of claim 1 , wherein the included angle “Ω” of adjacent second brushes satisfies the formula: Ω=β+K*α, wherein α=360/M, and K is an integer.

5. The motor of claim 1 further comprising a third brush and a switch, wherein the commutator comprises a second conductive ring spaced from the first conductive ring and plurality of second bars extending from the second conductive ring, the first bars and second bars are alternately arranged along a path of the second brushes; the third brush is arranged to make continuous sliding electrical contact with the second conductive ring; the first and third brushes are electrically connected to the first terminal of the direct current power source via the switch, the switch being configured to selectively connect either the first brush or the third brush to the first terminal of the direct current power source.

6. The motor of claim 5 , wherein the commutator has a cylindrical brush contact surface formed by the first and second conductive rings and the first and second bars extending in the axial direction of the shaft.

7. The motor of claim 5 , wherein the rotor poles are made of ferromagnetic material.

8. The motor of claim 7 , wherein the number of the teeth is equal to the number of coils and each coil is wound about a single respective tooth, and P is equal to N minus two or to N plus two.

9. The motor of claim 8 , wherein transition pads are disposed in the contact path of the second brushes between the first bars and the second bars to form a sliding contact surface for the second brushes.

10. The motor of claim 1 , wherein the number of the teeth is equal to N multiplied by the number of coils that generate a magnetic field when a single phase is energized, and P is equal to N minus two or to N plus two.

11. The motor of claim 5 , wherein the commutator has a planar brush contact surface formed by the first and second conductive rings and the first and second bars extending in the radial direction of the shaft.