Motor having concentratedly-wound stator coil

1. A motor comprising:

a rotor; and

a stator opposed to the rotor with a radial gap or an axial gap formed therebetween, the stator including a plurality of pole cores and a stator coil comprised of a plurality of unit coils each of which is concentratedly wound around a corresponding one of the pole cores,

wherein

each of the unit coils is comprised of a pair of first and second sub-coils that are stacked in two layers in a stacking direction, the stacking direction coinciding with a height direction of the corresponding pole core,

each of the first and second sub-coils is spirally wound so that coil sides of the sub-coil overlap each other in an overlapping direction perpendicular to the stacking direction,

each of the unit coils also has, at a single place, a connecting portion that connects the first and second sub-coils of the unit coil,

the connecting portion is provided in a coil end of the unit coil,

for each of the first and second sub-coils of the unit coil, the connecting portion is located at an innermost periphery of the sub-coil in the overlapping direction of the sub-coil, and

for each of the unit coils, the connecting portion of the unit coil has its thickness set to be less than the thickness of other portions of the unit coil in the overlapping direction.

2. The motor as set forth in claim 1 , wherein for each of the unit coils, the connecting portion of the unit coil has its thickness set to be substantially ½ of the thickness of the other portions of the unit coil in the overlapping direction and its width set to be substantially twice the width of the other portions of the unit coil in the stacking direction.

3. The motor as set forth in claim 1 , wherein each of the first and second sub-coils of the unit coils has a quadrangular cross section.

4. The motor as set forth in claim 1 , wherein the motor is a DC motor where the stator constitutes an electromagnet-type field and the rotor constitutes an armature,

for each of the unit coils, an outermost coil side of the first sub-coil of the unit coil, which is connected with a winding finish end of the first sub-coil, constitutes a first lead portion of the unit coil, and an outermost coil side of the second sub-coil of the unit coil, which is connected with a winding finish end of the second sub-coil, constitutes a second lead portion of the unit coil, and

each of the first and second lead portions of the unit coils is arranged to adjoin, either in the overlapping direction or in the stacking direction, another one of the first and second lead portions of the unit coils, and

each adjoining pair of the first and second lead portions of the unit coils are electrically connected with each other.

5. The motor as set forth in claim 1 , wherein the motor is used in a starter for starting an internal combustion engine.