Brushless motor and electric power steering system

1. A brushless motor having a magnetic flux density which is not saturated at a maximum current, comprising:

a rotor which has ten permanent magnets each containing rare earth neodymium and provided around a rotor yoke and an outside diameter of 45 mm to 55 mm, and

a stator which has a stator core having twelve slots and an outside diameter of 75 mm to 85 mm and whose magnetomotive force at maximum current is 700 AT or more without substantial saturation of the magnetic flux density,

wherein a teeth width of the stator core is 0.14 times or more of the outside diameter of the rotor.

2. A brushless motor according to claim 1 , wherein a slot opening width of the stator core is 0.5 mm or more.

3. A brushless motor according to claim 1 , wherein a yoke width of the stator core is 45% or more of the teeth width.

4. A brushless motor according to claim 1 , wherein each of the permanent magnets has a thickness of 2 mm or more in a radial direction of the rotor.

5. A brushless motor according to claim 1 , wherein the stator core is made up of an electromagnetic steel sheet whose magnetic flux density is 1.79 T when a magnetizing force is 10000 A/m.

6. A brushless motor according to claim 1 , wherein a minimum radial thickness of the rotor yoke is 5 mm or more when a residual magnetic flux density of the permanent magnet is 1.30 T or more.

7. An electric power steering system comprising:

a torque sensor for detecting a steering torque applied to a steering member of a vehicle; and

a brushless motor according to claim 1 ,

wherein the brushless motor is driven according to a steering torque detected by the torque sensor so as to assist a steering operation.