The subj ect of the present invention is a monophase electric induction motor with proj ecting poles and with a plurality of speeds , according to the preamble of the main claim .

As is known, motors of the monophasic electric induction type have various uses ; their use is widespread inside kitchen extractor hoods , and in particular in the extractor fan of these hoods which can extract fumes , vapours and grease which are generated on a cooking hob of a kitchen during the preparation of food . This is because said electric motors can operate with different speeds such as to allow the corresponding extractor fans to operate at different rates which can be selected by the users according to the needs .

A conventional electric induction motor comprises a stator and a rotor which rotates inside it . The stator is defined by an annular set of plates , from the inner perimeter of which there proj ect four poles or polar expansions which are connected to the set of plates at a first end thereof , and face the rotor with their second, free end .

The polar expans ions pass through corresponding supports of a winding of an electrical conductor, which is usually made of copper, said supports usually being indicated by the term "cartouche" , which will be used hereinafter in order to indicate the supports themselves . Each cartouche comprises a body with two flat opposite faces , between which there is present an intermediate element , which, together with these faces , defines a notch on which the winding of the electrical conductor is present . This body is usually polygonal , and comprises an axial hole in which a corresponding polar expansion is present , through which hole it passes .

The cartouches are then positioned around the inner perimeter of the set of plates in a manner which is consecutive and adj acent to one another . The cartouches normally define two identical pairs for the electrical windings , which pairs are placed opposite and in quadrature with one another, such as to define a first pair of stator windings defined as the "main" pair, and a second pair of stator windings defined as the "auxiliary" pair . The first pair is connected directly to the network, whereas the second is connected indirectly to the network by means of interposition of an offset capacitor, connected in series .

Each pair of windings ( or coils ) is positioned within the stator, after insertion of the corresponding polar expansions into the cartouches .

Although the known solutions for motors of the aforementioned type permit desired variation of the speed of operation of the corresponding extractor fans , they nevertheless have room for improvement .

In particular, the obj ective of the present invention is to provide an induction motor with proj ecting poles which has improved efficiency compared with the corresponding known motors , in particular at low and average speeds .

Another obj ective is to provide a motor of the aforementioned type which makes possible an increase in the energy efficiency, and consequent saving of energy during use .

A further obj ective is to provide a motor of the aforementioned type which makes possible better electrical insulation between the windings .

These obj ectives and others , which will become apparent to persons skilled in the art , are achieved by an electric induction motor with proj ecting poles according to the appended claims . For better understanding of the present invention, purely by way of non-limiting example , the following drawings are appended, in which : figure 1 shows a view in perspective of a motor produced according to the invention ; figure 2 shows an exploded view in perspective of the motor in figure 1 ; figure 3 shows a view in transverse crosssection of the motor in figure 1 ; figure 4 shows a view in perspective of the motor in figure 1 with some parts omitted for the sake of greater clarity; and figure 5 shows an exploded view in perspective of what is represented in figure 4 .

With reference to the aforementioned figures , an electric induction motor with proj ecting poles is generally indicated as 1 , and comprises a stator 2 and a rotor 3 keyed onto output shaft 4 . The stator and the rotor are enclosed by external closure elements defined by a bottom 5 and a cover 6 which are connected by means of screws 7 ; this bottom and cover have respective openings 10 and 11 for passage of the output shaft 4 where bearings or bushes 12 and 13 are placed .

A board 26 with a printed circuit 17 permits the supply and connection between the various outlets of the windings .

More particularly, the stator 2 comprises an annular set of plates 20 with a polygonal shape , having an inner perimeter P which is defined by consecutive sides 20A, 20B, 20C and 20D . The sides contain a slot ( in the form of a dovetail , for example ) 21 which can contain and retain a first end 22 of a corresponding polar expansion 23 which proj ects from the respective side of the perimeter P towards the inside of the stator . Each polar expansion has a second, free end 24 , placed in the cavity 25 of the stator frontally relative to the rotor 3 .

Along the sides 20A-D of the perimeter P of the annular set of plates 20 , there are placed cartouches 30A, 30B, 30C, 30D which can support conductor windings 31 defined by a copper wire wound around an intermediate element 33 of a respective cartouche . More particularly, each cartouche 30A-D (made of any insulating material ) comprises a body 34 defined by opposite and spaced flat faces 35 , 36 , between which the intermediate element 33 is present . Between these faces a slot is present , in which slot the winding 31 is present . Opposite cartouches are the same as one another, but are different from the adj acent and consecutive cartouches . In particular, the cartouches indicated as 30A and 300 in the figures , defining a first pair of cartouches , have larger dimensions than the cartouches 30B, 30D of a second pair of cartouches present inside the cavity 25 of the set of plates 20 , and contain a quantity ( and density) of conductive material which is greater than that present between the cartouches 30B, 30D of the second pair of cartouches . This greater quantity can be obtained by means of a larger number of turns of the windings made of conductive material present on the intermediate element 33 of the cartouches 30A, 30 D, or, the windings 31 which are present on this intermediate element can be obtained by means of wires with a larger cross-section than the wires of the windings present on the intermediate elements of the cartouches 30B, 30D of the second pair of cartouches .

In addition, the cartouches 30A, 30C have their flat face 35 with a larger area than the opposite and spaced face 36, said flat face 35 being the face of the cartouche which is furthest inside the cavity 25 . The face 36 is supported on the respective side 20A-D of the inner perimeter P of the annular set of plates 20 . The presence of the flat faces 35 with a larger area makes it possible to close the adj acent intermediate elements 33 of the cartouches 30B and 30D laterally ( see figure 3 ) thus insulating the windings which are present thereon against those of the cartouches .

On the other hand, the elements 33 inside the cartouches 30A and 300 are closed laterally by proj ecting angular arms 41 which rise from the bottom 5 at corners thereof . These arms penetrate inside the lateral ends 64 of the cartouches 30A and 300 of the first pair of cartouches , thus insulating the winding present therein .

The cartouches 30A-D have a through-hole 53 which accommodates a corresponding polar expansion .

Since the pair of cartouches 30A, 300 have different dimensions ( transverse length, measured parallel to the corresponding sides of the annular stator set 20 , of their intermediate elements ) from the other pair of cartouches 30B, 30D, it is possible to position inside the cartouches 30A, 300 a different density of windings ( a larger number or with an increased cross-section) from that of the other two cartouches 30B, 30D, thus making it possible to obtain greater efficiency and control of the minimum and average speed of rotation of the rotor 3 ( and therefore of the extractor fan with which the motor 1 is associated) than that which can be obtained with the known motors of the prior art .

A description has been provided of a preferred embodiment of the invention . It will be appreciated that others are also possible ( such as the one where the faces 35 and 36 of the cartouches 30A, 30C are the same , and larger than the corresponding faces of the remaining cartouches 30B, 30D) , and must be considered as included in the scope of the invention as defined by the following claims .