Electric machine

1. An electric machine, comprising:

a rotor having at least one pole pair, the at least one pole pair including a first magnetic pole and a second magnetic pole having opposite polarities, wherein

the first magnetic pole includes a first inner radial permanent-magnet layer and a first outer radial permanent-magnet layer,

the second magnetic pole includes a second inner radial permanent-magnet layer and a second outer radial permanent-magnet layer,

an angle δ 2 measured from a rotation axis of the rotor between an outer end of the first inner radial permanent-magnet layer and an outer end of the second inner radial permanent-magnet layer has a value of between about 27 and about 55 electrical degrees; and

a stator having a stator core with an odd number of stator slots per pole pair of the rotor.

2. The electric machine of claim 1 , wherein the angle δ 2 has a value of between about 30 and about 40 electrical degrees.

3. The electric machine of claim 2 , wherein the stator core includes nine stator slots per pole pair of the rotor.

4. The electric machine of claim 2 , wherein an angle δ 1 measured from a rotation axis of the rotor between the outer end of the first inner radial permanent-magnet layer and an adjacent outer end of the first outer radial permanent-magnet layer has a value of between about 27 and about 55 electrical degrees.

5. The electric machine of claim 1 , wherein an angle δ 1 measured from a rotation axis of the rotor between the outer end of the first inner radial permanent-magnet layer and an adjacent outer end of the first outer radial permanent-magnet layer has a value of between about 27 and about 55 electrical degrees.

6. The electric machine of claim 1 , wherein the angle δ 1 has a value of between about 30 and about 40 electrical degrees.

7. The electric machine of claim 1 , wherein an axis of a first portion of the first inner radial permanent-magnet layer and an axis of a first portion of the first outer radial permanent-magnet layer diverge from one another as they extend into the rotor.

8. A method of operating an electric machine, comprising:

generating magnetic flux with at least one pole pair of a rotor of the electric machine, wherein

the at least one pole pair includes a first magnetic pole and a second magnetic pole having opposite polarities,

the first magnetic pole includes a first inner radial permanent-magnet layer and a first outer radial permanent-magnet layer,

an axis of a first portion of the first inner radial permanent-magnet layer and an axis of a first portion of the first outer radial permanent-magnet layer diverge from one another as they extend into the rotor;

the second magnetic pole includes a second inner radial permanent-magnet layer and a second outer radial permanent-magnet layer;

an angle δ 2 measured from a rotation axis of the rotor between the outer end of the first inner radial permanent-magnet layer and an outer end of the second inner radial permanent-magnet layer has a value of between about 27 and about 55 electrical degrees; and

generating magnetic flux with a stator of the electric machine, wherein the stator of the electric machine includes a stator core with an odd number of stator slots per pole pair of the rotor.

9. The method of claim 8 , wherein an angle δ 1 measured from a rotation axis of the rotor between the outer end of the first inner radial permanent-magnet layer and an adjacent outer end of the first outer radial permanent-magnet layer has a value of between about 27 and about 55 electrical degrees.

10. The method of claim 9 , wherein the stator core includes nine stator slots per pole pair of the rotor.

11. The method of claim 8 , wherein an angle δ 1 measured from a rotation axis of the rotor between the outer end of the first inner radial permanent-magnet layer and an adjacent outer end of the first outer radial permanent-magnet layer has a value of between about 27 and about 55 electrical degrees.

12. The method of claim 8 , wherein an axis of a second portion of the first outer radial permanent-magnet layer and an axis of a second portion of the first inner radial permanent-magnet layer diverge from one another as they extend into the rotor.

13. An electric machine, comprising:

a rotor with at least one pole pair, the at least one pole pair including a first magnetic pole and a second magnetic pole with opposite polarities, wherein

the first magnetic pole includes a first inner radial permanent-magnet layer and a first outer radial permanent-magnet layer, and

an angle δ 1 measured from a rotation axis of the rotor between an outer end of the first outer radial permanent-magnet layer and an adjacent outer end of the first inner radial permanent-magnet layer has a value of between about 27 and about 55 electrical degrees;

the second magnetic pole includes a second inner radial permanent-magnet layer and a second outer radial permanent-magnet layer, and

an angle δ 2 measured from a rotation axis of the rotor between an outer end of the first inner radial permanent-magnet layer and an outer end of the second inner radial permanent-magnet layer has a value of between about 27 and about 55 electrical degrees; and

a stator with a stator core that has an odd number of stator slots per pole pair of the rotor.

14. The electric machine of claim 13 , wherein an axis of a first portion of the first inner radial permanent-magnet layer and an axis of a first portion of the first outer radial permanent-magnet layer diverge from one another as they extend into the rotor.

15. The electric machine of claim 14 , wherein the stator core includes nine stator slots per pole pair of the rotor.

16. The electric machine of claim 15 , wherein the angle δ 1 has a value of between about 30 and about 40 electrical degrees.

17. The electric machine of claim 13 , wherein the angle δ 1 has a value of between about 30 and about 40 electrical degrees.

18. The electric machine of claim 13 , wherein the stator core includes nine stator slots per pole pair of the rotor.