The majority of the direct drive motor systems for washing machines, either front loading or top loading washing machines have the stator core formed from a continuous helically wound metallic strip having a plurality of teeth defined between formed in one edge thereof.
In those washing machines, the weight of the overall motor system is increased by the material needed for assuring a mechanical continuity between the teeth. Additionally, this kind of construction cannot be used for the dual rotor type motor, in which the rotor assembly presents an outer crown-shaped portion with a first series of magnets secured along a circumferential direction and an inner crown-shaped portion with a second series of magnets.
A direct drive motor system for a washing machine having dual rotor type motor is disclosed by WO 2006/075903. In this document the stator presents a plurality of single partition cores formed in a double T shape, each formed by stacked laminations and provisionally connected, during the assembly process of the stator, by means of two circular insulators connected each other in order to obtain one single element. A similar direct drive motor system is disclosed by U.S. Pat. No. 6,992,419 in which the stator is fabricated with a number of individual cores which are then integrally formed into a single body in annular form via an insert molding using thermosetting resin. Even if these known solutions solve the problem of providing a stator for a dual rotor type motor, nevertheless the process of assembling the stator is quite complex, since after having mounted the single cores between the two insulators and after having wound the coils around the insulators, this not yet finished component is put in a metal mold and resin is injected for producing a quite complex molding part having also a portion for fixing the stator to the tub or to the motor securing tub. The complex assembly process and the use of a polymer increases the overall cost of the direct drive motor system, particularly because the polymer must have certain mechanical characteristic in order to guarantee a dimensional stability of the stator. This means that low cost thermoplastics polymers like polypropylene cannot be used. Usually the higher the mechanical features of the polymer, the higher the temperature of the injection molding process. This can lead to problems of a higher melting point of the resin compared to that of the enamel of the coil as well as that of the insulator material, with possible damages of both.