Universal motor with auxiliary magnetic poles

1. A universal motor comprising:

a stator and a rotor rotatably installed in the stator,

wherein the rotor comprises a rotor core and rotor windings wound on the rotor core, wherein the stator comprises a stator core having a yoke, n primary poles with windings wound thereon and n auxiliary poles, the primary poles and auxiliary poles being alternately arranged at the radially inner side of the yoke in a circumferential direction thereof, the auxiliary poles being without windings wound thereon or with additional windings wound thereon, the number of turns of the additional windings being less than that of the windings wound on the primary poles; and

wherein when the windings are electrified, n primary magnetic poles and n auxiliary magnetic poles are formed at the primary poles and auxiliary poles respectively and 2n magnetic circuits are formed, each primary magnetic pole has the same polarity and each auxiliary magnetic pole has the same polarity which is opposite the polarity of the primary magnetic poles, n being an integer greater than 1, each of the magnetic circuits passing through a primary magnetic pole and an adjacent auxiliary magnetic pole and corresponding portions of the rotor and yoke such that the length of the magnetic circuit is reduced and the torque produced by the motor is increased.

2. A universal motor comprising:

a stator and a rotor rotatably installed in the stator,

wherein the rotor comprises a rotor core and rotor windings wound on the rotor core, wherein the stator comprises a stator core having a yoke, n primary poles with windings wound thereon and n auxiliary poles, the primary poles and auxiliary poles being alternately arranged at the radially inner side of the yoke in a circumferential direction thereof;

wherein when the windings are electrified, n primary magnetic poles and n auxiliary magnetic poles are formed at the primary poles and auxiliary poles respectively and 2n magnetic circuits are formed, each primary magnetic pole has the same polarity and each auxiliary magnetic pole has the same polarity which is opposite the polarity of the primary magnetic poles, n being an integer greater than 1, each of the magnetic circuits passing through a primary magnetic pole and an adjacent auxiliary magnetic pole and corresponding portions of the rotor and yoke such that the length of the magnetic circuit is reduced and the torque produced by the motor is increased; and

wherein the ratio of the outer diameter D of the rotor to the minimum outer diameter Y of the stator core D/Y is greater than 0.7.

3. The universal motor of claim 1 , wherein the auxiliary poles are without windings wound thereon and the auxiliary magnetic poles are induced magnetic poles.

4. The universal motor of claim 1 , wherein the yoke comprises first sections from which the primary poles extend, and second sections from which the auxiliary poles extend, the first sections being narrower than the second sections in radial directions of the yoke.

5. The universal motor of claim 4 , wherein mounting holes are formed in the second sections.

6. The universal motor of claim 1 , wherein the primary poles and the auxiliary poles are salient poles projecting inwardly from the yoke, each pole comprises a neck inwardly extending from the yoke and a pole shoe extending from the neck, the distance between the yoke and the pole shoes of the primary poles is greater than the distance between the yoke and the pole shoes of the auxiliary poles.

7. The universal motor of claim 6 , wherein additional windings are wound on the auxiliary poles, the number of turns of the additional windings being less than that of the windings wound on the primary poles.

8. The universal motor of claim 6 , wherein in the circumferential direction, the necks of the primary poles are narrower than the necks of the auxiliary poles.

9. The universal motor of claim 1 , wherein n is equal to 2, 3, or 4.

10. The universal motor of claim 1 , wherein the radial gap between the primary poles and the rotor core is equal to the radial gap between the auxiliary poles and the rotor core.

11. The universal motor of claim 1 , wherein the cross section of the stator core has a rectangular shape.

12. The universal motor of claim 11 , wherein the ratio of the outer diameter D of the rotor to the length of a line between two points of the periphery of the stator core passing through the axial center of the stator and the auxiliary poles is greater than 0.7.

13. A universal motor comprising:

a stator and a rotor rotatably installed in the stator,

wherein the rotor comprises a rotor core and rotor windings wound on the rotor core,

wherein the stator comprises a stator core having a yoke, n primary poles each with a single coil wound thereon and n auxiliary poles, the primary poles and auxiliary poles being alternately arranged at the radially inner side of the yoke in a circumferential direction thereof, each coil only wound on a single pole, each auxiliary pole being without coil wound thereon or with an additional coil wound thereon, the number of turns of the additional coil being less than that of the coil wound on the primary pole,

wherein when the windings are electrified, n primary magnetic poles and n auxiliary magnetic poles are formed at the primary poles and auxiliary poles respectively, each primary magnetic pole has the same polarity and each auxiliary magnetic pole has the same polarity which is opposite the polarity of the primary magnetic poles, n being an integer greater than 1, every two adjacent primary magnetic pole and auxiliary magnetic pole forming a magnetic circuit passing through portions of the rotor to cause the rotor to rotate; and

wherein the primary poles and the auxiliary poles are salient poles projecting inwardly from the yoke, each pole comprises a neck inwardly extending from the yoke and a pole shoe extending from the neck, the distance between the yoke and the pole shoes of the primary poles is greater than the distance between the yoke and the pole shoes of the auxiliary poles.

14. The universal motor of claim 13 , wherein in the circumferential direction the necks of the primary poles are narrower than the necks of the auxiliary poles.

15. A universal motor comprising:

a stator and a rotor rotatably installed in the stator,

wherein the rotor comprises a rotor core and rotor windings wound on the rotor core,

wherein the stator comprises a stator core having a yoke, n primary poles each with a single coil wound thereon and n auxiliary poles, the primary poles and auxiliary poles being alternately arranged at the radially inner side of the yoke in a circumferential direction thereof, each coil only wound on a single pole,

wherein when the windings are electrified, n primary magnetic poles and n auxiliary magnetic poles are formed at the primary poles and auxiliary poles respectively, each primary magnetic pole has the same polarity and each auxiliary magnetic pole has the same polarity which is opposite the polarity of the primary magnetic poles, n being an integer greater than 1, every two adjacent primary magnetic pole and auxiliary magnetic pole forming a magnetic circuit passing through portions of the rotor to cause the rotor to rotate;

wherein the primary poles and the auxiliary poles are salient poles projecting inwardly from the yoke, each pole comprises a neck inwardly extending from the yoke and a pole shoe extending from the neck, the distance between the yoke and the pole shoes of the primary poles is greater than the distance between the yoke and the pole shoes of the auxiliary poles;

wherein the cross section of the stator core has a rectangular shape, and the ratio of the outer diameter D of the rotor to the length of a line between two points of the periphery of the stator core passing through the axial center of the stator and the auxiliary poles is greater than 0.7.