This invention relates to the armature of a direct current (d.c.) motor whose armature coils are of wave winding type.
FIG. 3 is an developmental view of an armature coil of a conventional d.c. motor. The armature coil 1 is of a wave winding type, and has a straight portion 1b of the lower coil and a straight portion 1d of the upper coil, which are connected together through a rear head portion 1c, and a connecting leg portion 1a of the lower coil and a connecting leg portion 1e of the upper coil which are extended from the straight portions 1b and 1d. The motor has a plurality of armature coils 1; that is, the number of armature coils 1 is equal to the number of slots in the armature core. The lower straight portions 1b and the straight portion 1d are inserted into the slots of the armature core successively. In general, the commutator bars of the commutator are equal in number to the slots. For instance, in the case of a wave winding of six poles and twenty-eight slots, the number of the commutator bars is twenty-eight (28). The lower connecting leg portions 1a and the upper connecting leg portions 1e of the armature coils 1 are connected to the respective commutator bars by soldering, thus forming an armature winding of a wave winding type.
In the above-described conventional d.c. motor's armature, the number of the commutator bars is equal to that of the slots in the armature core. When, because of the characteristic of an electric motor, the number of armature slots is increased. It is necessary to increase the number of commutator bars, and accordingly to decrease the thickness of the brushes. If the thickness of the brushes is decreased excessively, the mechanical strength is decreased, and the service life is also shortened. If, on the other hand, the brush thickness is increased, it is necessary to increase the thickness of the commutator bars. In this case, the commutator is increased in outside diameter, the armature is also increased in outside diameter, and the brush device is increased in radial dimension. Thus, the resultant motor is increased in outside diameter.
If, in the case where the increase in outside diameter of the motor is limited, it is necessary to increase the outside diameter of the commutator, then it is necessary to decrease the height of the brushes also. This decrease will reduce the service life of the brushes.