Electric motor

1. A universal motor comprising a stator and a rotor installed in the stator, the stator comprising:

a pair of identical stator segments, each segment comprising a yoke having first and second ends, a pole and a neck connecting the pole to the first end of the yoke, each pole having two opposite ends in a circumferential direction of the rotor, the first end of the yoke having a first planar end surface, the second end having a second planar end surface which is oppositely arranged relative to the first planar end surface, the first and second planar end surfaces being inclined relative to an axial plane passing through a center of the pole, one of the first and second planar end surfaces having a groove and the other one having a projecting rib, the projecting rib on each yoke being engaged in the groove of the other yoke, and the first planar end surface of each yoke being in contiguous contact with the second planar end surface of the other yoke; and

a pair of pre-formed windings mounted on respective poles of the stator segments.

2. The motor of claim 1 , wherein the groove and the projecting rib of each yoke are oppositely arranged relative to each other.

3. The motor of claim 1 , wherein the groove and the projecting rib of each yoke are inclined towards the axial plane passing through the center of the pole.

4. The motor of claim 1 , wherein the first planar end surface of each yoke extends from a point at the respective pole to a point at an outer surface of the yoke and has a length in the extending direction greater than the greatest radial width of the yoke so that the magnetic flux density at the first planar end surface is smaller than other places of the yoke.

5. The motor of claim 1 , wherein each of the two opposite ends of each pole has a straight edge in the axial direction of the motor.

6. The motor of claim 1 , wherein each winding is received in a receiving space defined by the respective pole, associated neck and adjacent portions of the two yokes.

7. The motor of claim 6 , wherein parts of the windings extend beyond the respective receiving spaces.

8. The motor of claim 6 , wherein the first planar end surface is located at a closed end of a respective receiving space and inclined relative to the circumferential direction of the stator.

9. The motor of claim 1 , wherein the two stator segments are welded together.

10. The motor of claim 1 , wherein the projecting rib on each yoke is pressed into the groove of the other yoke.

11. A universal motor comprising a stator and a rotor installed in the stator, the stator comprising:

a pair of identical stator segments, each segment comprising a yoke having first and second ends, a pole and a neck connecting the pole to the first end of the yoke, each pole having two opposite ends in a circumferential direction of the rotor and a pole surface confronting the rotor, the first end of the yoke having a first planar end surface formed at an outer surface thereof which is opposite to the pole surface, the second end having a second planar end surface formed at an inner surface thereof, the first and second planar end surfaces being inclined relative to an axial plane passing through a center of the pole, one of the first and second planar end surfaces having a groove and the other having a projecting rib, the projecting rib on each yoke being engaged in the groove of the other yoke, and the first planar end surface of each yoke being in continuous contact with the second planar end surface of the other yoke; and

a pair of pre-formed windings mounted on respective poles of the stator segments.

12. The motor of claim 11 , wherein the projecting rib extends from the first or second planar end surface in a direction which is inclined relative to the circumferential direction of the stator.