Background of the Invention Known induction electric motors comprise a stator in the form of a stack of laminations provided with grooves, which lodge the coil turns. Close to the inner diameter of the stator, these grooves are half- closed, leaving a passage denominated receiving housing opening, through which are inserted the coil turns.

The electric motor has a main magnetic field, which crosses an air gap when passing from the stator to the rotor and vice-versa.

This main magnetic field is sinusoidal, according to the frequency of the electrical network. To this sinusoidal wave is superposed a pulsation, which is a function of the receiving housing opening and which produces iron losses, mainly in the teeth of the juxtaposed laminations of the stator, said losses varying exponentially as a function of the receiving housing opening. Moreover, the opening of the groove increases the electric current, which is necessary to keep the sinusoidal magnetic field required by the motor, increasing the losses in the motor coils.

The receiving housing opening represents an irregularity in the magnetic length of the air gap, since the optimum condition would be that in which the groove is completely closed, producing a single constant distance.

Regarding the torque curve, this groove opening is necessary, otherwise the reactances of the groove top would be greatly increased; in this case, said opening

is a direct function of the magnetic permeability of the metallic means which will always be higher than the value of the air magnetic permeability, about up to 10.000 times higher.

In order to combine these two phenomena, which vary inversely, a half-closed groove with a minimum groove opening can be used, which will be posteriorly closed with a saturable magnetic material.

In a known solution, closing of each longitudinal alignment of grooves in the lamination stack of the stator is achieved by providing each said alignment with a respective insert made of soft ferrite, which is fitted and retained in the inner portion adjacent to the opening of each groove of said alignment. The use of the soft ferrite allows to obtain an insert which, by magnetically connecting the ends of the longitudinal opening of each groove alignment, has minimum losses.

By using an insert in soft ferrite, the magnetic field, in low currents, considers the receiving housing opening closed. With high currents, the ferrite is saturated, resulting in a low reactance at the groove top, similar to the reactance of a half- closed receiving housing opening.

However, in low power motors, these inserts are very thin and fragile, making difficult to handle them in these dimensions.

Another disadvantage is that the insert constitutes one more component, besides requiring the stator to be impregnated with resin, in order to avoid vibration of said insert, which may generate noise and release of insert fragments due to wear caused by attrition resulting from magnetic vibration.

Another option is to cast inside the grooves, a ferrite-resin compound, with the same characteristics

of the ferrite insert, since this agglomerate turns into a soft ferrite, which has the advantage of being rigidly affixed to the lamination stack after curing.

The disadvantage of the compound is its difficult application in the plurality of grooves, since the application is necessarily obtained by injection, the cure occurring in a short period of time and with a high solid content, so that the shape is not very much altered after curing, the inner diameter of the stator remaining the more perfect as possible. Moreover, the viscosity of the injected compound should be low, in order to prevent said compound from leaking through the inner diameter of the stator.

Disclosure of the Invention Thus, it is an objective of the present invention to provide an electric motor stator, which comprises a receiving housing opening for coil turns with a larger width than that of the receiving housing openings of the prior art, allowing the respective groove to be filled more easily and with more coil turns, allowing the use of coil turns with a larger diameter and providing an opening closing which avoids the occurrence of long path eddy currents in the stator, improving the efficiency of the motor, without the deficiencies of the prior art constructions.

This objective is attained by an electric motor stator, comprising a tubular lamination stack, including a plurality of annular laminations, each having a plurality of grooves with a receiving opening provided in a radially internal edge of said annular lamination; a coil defined by multiple coil turns introduced in the grooves; and groove closing elements, each groove of each annular lamination incorporating, in a single piece, from at least one edge of the respective receiving opening, a closing

element, which is deformable between an open position, unblocking the respective receiving opening for introducing coil turns, and a closed position, reducing the width of the respective receiving opening to a value which, during the operation of the motor in low currents, allows the magnetic field to consider said receiving opening closed.

Thus, it is possible to design an induction electric motor, particularly of low power which, besides overcoming the prior art disadvantages, allows the introduction of coil turns with large diameters inside the grooves and further allows, after the conductors have been inserted, the groove ends to be totally or partially closed, reducing the magnetizing electric currents and consequently the heating due to losses, and increasing the efficiency of the motor.

The present invention further allows a larger amount of wires inside the grooves (higher filling factor), due to the easy insertion of said wires, consequently increasing the energetic efficiency of the motor.

Brief Description of the Drawings The invention will be described below, with reference to the attached drawings, in which: Figure 1 is a partial cross-sectional view of an electric motor stator, illustrating part of a lamination of a lamination stack of said stator, with a groove of said lamination being filled with coil turns, said stator being constructed according to the prior art; Figure 2 illustrates, schematically and partially, an enlarged view of an annular lamination, which has part of its grooves provided with coil turns and which is constructed according to the prior art; Figure 3 illustrates, schematically and partially, an enlarged view of an annular lamination, which is

constructed according to the present invention and which is opened to allow the insertion of coil turns therein; and Figure 4 illustrates, schematically and partially, the groove of figure 3 closed, after the coil turns have been inserted therein.

Best Mode of Carrying Out the Invention According to the illustrations, the present invention refers to an electric motor stator, having a tubular stack of annular laminations 1 and a coil defined by a plurality of coil turns 2, which are inserted and retained in the tubular lamination stack, as described below.

According to the prior art, which is illustrated in figures 1 and 2, each annular lamination 1 includes a plurality of grooves 3, which are circumferentially provided in each annular lamination 1, each groove 3 having a receiving opening 4, which is provided from a radially internal edge of the annular lamination 1 and through which is progressively introduced a determined pre-established amount of coil turns 3, in order to form the coil of the present stator.

Each receiving opening 4 defines a coil turn feeding channel, for a respective groove 3, with a width which is determined so as to allow the simultaneous introduction of a determined quantity of coil turns 2 inside groove 3.

Each longitudinal alignment of grooves 3 defines a coil turn receiving housing, which receives before introducing the corresponding coil turns, an insulating liner 5, which avoids the direct contact of the coil turns 2 with the abrasive material of the annular lamination 1, thus avoiding scratches in the insulating enamel of each coil turn 2. After finishing the insertion of the coil turns inside each receiving

housing, it is also introduced into the latter a closing element 6, which is also insulating and which closes each said receiving housing.

According to the prior art, each closing element 6 is in the form of a continuous body, with a longitudinal extension coinciding with that of the tubular lamination stack, which has a"U"shaped transversal profile and which is provided inside each corresponding coil turn receiving housing, adjacent to the alignment of receiving openings 4 of grooves 3 which define said coil turn receiving housing, after the introduction of said coil turns 2 inside the latter.

This construction has the disadvantage discussed above.

According to the present invention, closing of each groove 3 of an annular lamination 1, after a determined quantity of coil turns 2 has been inserted inside a longitudinal alignment of grooves 3, is achieved by providing each groove with at least one closing element 10 projecting from a respective radially internal edge of the annular lamination 1 preferably from a weakening line E, which is defined in said edge and which permits the corresponding closing element 10 to have an open position, unblocking the respective receiving opening 4 for the introduction of coil turns 2 inside the corresponding groove 3, and a closed position, when the width of the receiving opening 4 of each groove 3 is diminished to a value which, during the operation of the motor in low currents, allows the magnetic field to consider said receiving opening 4 closed. In a particular constructive option, the closed position of each closing element 10 completely closes the respective receiving opening 4.

The reduction of the receiving opening 4 upon closing the respective groove 3 allows to reduce the irregularities in the magnetic length, resulting in lower magnetizing current, lower load current and less losses due to Joule effect in the primary winding.

According to the illustrations in figures 3 and 4, each groove 3 incorporates a closing element 10, axially projecting towards one of the sides of the plane of the respective annular lamination 1, in its open position, the closed position being obtained, by appropriate means, by said closing element 10 being angularly displaced, from said open position, around a rotation axis coinciding with the weakening line E mentioned above.

The closed position of each closing element 10 is achieved by the plastic deformation of said element around the weakening line E, after introducing the coil turns 2 in a longitudinal alignment of grooves 3 of the tubular lamination stack of the present stator.

After the coil turns have been introduced into each longitudinal alignment of grooves, said alignment also receives, when each groove 3 of said alignment has its respective closing element 10 in the closed position, a lining element, not illustrated, which is provided at the region of the receiving opening 4 and which avoids the contact of the coil turns 2 inside the grooves 3 with the material of the annular lamination 1.

According to another constructive form of the present invention, not illustrated, the open position of each closing element 10 is defined when the latter is coplanar to and radially projected towards the center of the respective annular lamination 1.

In either of the described embodiments, at least one of the open and closed positions is obtained by

plastic deformation of each closing element 10 around a rotation axis, for example coinciding with the weakening line E.

While an embodiment of a closing element has been described in the form of projection from one of the edges of a respective groove 3, other embodiments are possible within the concept presented, for example each groove 3 having a closing element 10 incorporated to each of the edges of the respective receiving opening 4.

The provision of individual closing elements 10 for each groove 3 of each annular lamination 1 avoids the formation of long trajectories for the eddy currents, since these elements form, along the longitudinal extension of the tubular stack of annular laminations of the stator, a discontinuous longitudinal closing element.

The present invention reduces significantly the pulsation superposed to the sinusoidal magnetic field, which passes through the stator crossing the air gap and consequently produces less iron losses on the laminations of the stator resulting from said pulsations, with a consequent reduction of energetic consumption and higher efficiency of the electric motor.