PURPOSE:To reduce the size and the weight by forming a plurality of blades on the core plates at the opposite sides of the inner circumference of coil and circulating the air by varying the direction of the blade while furthermore making a vent axially through the core at the position of the blade thereby cooling the bag space section, the interior of the core, commutator, and the like. CONSTITUTION:A plurality of blades 12 are formed at positions closer to the inner circumferential side than the slots to be buried with the coil 5 of a core plate 13 at the opposite ends of the core 4. Rised hole section serves as an air inlet/outlet and the air is circulated by varying the direction of the blades. A vent communicated to the side of a commutator insulator 6 is made through the core 4 sandwiched by the core plates 13 at the opposite ends. By such arrangement, the bag space 14, the interior of the core 4, the commutator 7, and the like can be cooled, and the size and the weight can be reduced.
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