Small-sized, AC series commutator motors (universal motors) are used very much in small appliances such as vacuum cleaners and hand tools, because they offer advantages of high speed and low cost. In particular, motors for vacuum cleaners are being designed with smaller size, but higher speed and increased output power. Therefore, it is desirable to improve commutation performance, because it influences the brush lifetime.
In this paper, a method to improve commutation performance of the motors is described. It is an exceptional armature winding form in which the turn number of the backward coil is less than that of the forward coil in the same slots. The commutation sequence determines which is the backward coil and which is the forward one. The configuration and operation of the exceptional armature winding form for universal motors are detailed. A factor to relate the commutation performance using the magnetic field and the commutation analyses is also described. The design theory is built up with respect to the exceptional armature winding form and usefulness of the method is verified for predicting brush lifetime with actual motors. The effect of the armature winding to improvement the brush lifetime is confirmed experimentally.