COOLING SYSTEM FOR AN ELECTRIC MACHINE AND ELECTRIC

MACHINE COMPRISING SAID STATOR

The present invention relates to a stator for an electric machine with a fluid inj ection cooling system and to an electric machine comprising said stator .

In particular, the invention refers to a stator for a closed-slot rotating electric machine , preferably with a continuous winding made using a metal blade , comprising a cooling system with oil inj ection directly into the closed slots , in particular into channels obtained close to said slots . Known electric machines include a fixed part , the stator , and a moving part , the rotor, coaxially arranged one inside the other . Typically, the rotor comprises a pack of laminations fixed on a rotation shaft , and is inserted inside the stator which includes an electric winding capable of generating a magnetic field that causes the rotor to rotate . The stator is generally annular m shape and includes a plurality of radial slots , inside which the electric winding is obtained .

From International Patent Application WO2016188764 , an electric machine with a stator with closed slots is known, for example a synchronous electric motor with reluctance assisted by permanent magnets , which provides a wall for closing the stator slots in correspondence with the rotor, to make closed slots that reduce the problems caused by torque ripple , with associated vibrations and noise .

For the reali zation of the electric windings of closed-slot stators , it is known to use electric conductors made using strips or continuous wires , or copper strips that are bent in the central part to form hairpin-shaped strips , to be inserted in the stator slots .

The shape and bending angles of the strips vary with the variation of the geometry of the stator and the slots , and with the variation of the winding scheme .

These strips are inserted into the stator slots according to a certain pattern, to obtain the exact number of turns necessary to compose the stator winding . A problem of known stators is caused by the thermal flux generated by the Joule ef fect when the winding is crossed by electric current : this heat flux must be evacuated to improve ef ficiency and prevent damage to the electric machine .

It is known to use cooling systems for electric motors ' stators , with oil that circulates in channels obtained in the external part of the stator .

These known cooling systems have the problem that oil circulates in the external part of the stator, distanced from the windings that represent the main heat source of the machine , reducing the efficiency of the heat exchange .

Another problem of known stator cooling systems is requiring to modi fy the stator in order to obtain the oil circulation channels close to the slots , increasing the design and production complexity .

Obj ect of the present invention is solving these problems by means of a stator with closed slots for an electric machine and an electric machine comprising said stator which allow to obtain a better efficiency of the electric machine by reali zing windings with greater active length, lower costs , better filling of the slots by the winding, also simpli fying the production process . Other obj ects of the present invention are the following : providing a high heat exchange between the cooling fluid and the motor windings ; improving the performance of an electric machine during continuous operations , increasing the performances duration before derating; improving the performance of the electric machine during peak operations , allowing to reach higher values of peak currents ; improving globally the electric machine ef ficiency; possibility of obtaining more powerful motors , with equal dimensions , compared to equivalent versions without the cooling system of the invention; obtaining a cool ing system which allows for less assembly and production complexity .

The aforementioned and other obj ects and advantages of the invention, which will appear from the following description, are achieved with a closed-slot stator for an electric machine and an electric machine comprising such a stator, as those described in the independent claims .

Preferred embodiments and non-trivial variants of the present invention are the subj ect matter of the dependent claims .

It is understood that all attached claims form an integral part of the present description . It will be immediately obvious that innumerable variations and modi fications ( for example relating to shape , dimensions , arrangements and parts with equivalent functionality) can be made to what i s described, without departing from the scope of the invention as appears from the attached claims .

The present invention will be better described by some preferred embodiments thereof , provided as a non-limiting example , with reference to the attached drawings , in which :

- FIG . 1 shows a perspective view of an internal part of a stator of an electric machine according to the invention;

- FIG . 2 shows a perspective view of an external part of a stator of an electric machine according to the invention;

- FIG . 3 shows a perspective view of a stator of an electric machine according to the invention;

- FIG . 4 shows a view of a continuous winding for a stator of an electric machine according to the invention;

- FIG . 5 shows a view of a plurality of continuous windings for a stator of an electric machine according to the invention;

- FIG . 6 shows a schematic front view of an internal part of a stator according to the invention;

- FIG . 7 shows a perspective view of an internal part of a stator with a continuous winding according to the invention;

- FIG . 8 shows a perspective view of a stator of an electric machine with a continuous winding according to the invention;

- FIG . 9 shows a perspective view of a rotor and a stator of an electric machine with a continuous winding according to the invention;

- FIG . 10 shows a partial schematic front view of a stator according to the invention;

- FIG . 11 shows a schematic front view of a closed slot of a stator according to the invention;

- FIG . 12 shows a block diagram of a closed-slots stator cooling system according to the invention .

With reference to the figures , the stator 15 with closed slots , preferably with continuous winding, will be described below for an electric machine according to the invention, which comprises a first internal stator part 25 comprising a plurality of longitudinal teeth 26 , spaced apart by a configured space 27 to make the lower part of the closed slots 14 of the stator, and a second external annular stator part 35 , preferably comprising a plurality of seats 36 complementary to the teeth 26 of the first stator part 25 and configured to associate with the first stator part 25 , in order to form the closed slots 14 and the stator 15 . Preferably, said seats 36 obtained in the second stator part 35 are configured to fit together with the teeth 26 of the first stator part 25 , in order to form a plurality of closed slots 14 of the stator, by means of a reciprocal sliding movement of the first internal stator part 25 and of the second external part 35 , for example along the direction o f the longitudinal Y axis of the stator 15 , reali zing a coupling, for example dovetail-type or other known type of coupling .

The closed slots 14 are arranged, preferably equidistant from each other, along a cylindrical internal wall 32 of the stator 15 configured to house a rotor 5 , and each slot 14 comprises a bottom wall 38 arranged in the direction of the longitudinal Y axis of the stator 15 , in proximity of the inner wall 32 at a distance E from said inner wall 32 and an upper wall 40 .

Said slots 14 are arranged along the direction of the longitudinal Y axis of the stator 15 and have an asymmetrical conformation with respect to a plane R passing through the longitudinal Y axis of the stator 15 and for a centreline P of the slot 14 in correspondence with the internal wall 32 ; preferably, the slots 14 have an asymmetrical conformation with respect to a plane R passing through the longitudinal Y axis of the stator 15 and through a centreline P of the bottom wall 38 .

Each closed slot 14 of the stator 15 is formed by two side walls 42 of two adj acent teeth 26 made in the first internal stator part 25 , by the bottom wall 38 connecting the two adj acent teeth 26 and by the upper wall 40 , preferably formed by a wall for connecting two adj acent seats 36 made in the second external stator part 35 ; for example , the bottom wall 38 has a semi-circular or arched shape .

In a preferred embodiment of the invention, the side walls 42 of a slot 14 are asymmetrical , in particular with respect to the plane R; preferably, the side walls 42 of the groove are curved or concave , and more preferably have the concavity made in such a way as to optimi ze the ef ficiency or operation of the electric machine in a desired operating direction; for example , the concavity faces in a speci fic direction with respect to a preferred rotation direction Z of the rotor 5 . As shown m Figures 10 and 11 , the closed-slots stator 15 for an electric machine according to the invention comprises : the closed slots 14 into which are inserted the conductors , preferably the straps 2 , forming the winding, overlapped starting with a lower conductor ( strap ) 5 in correspondence with the bottom wall 38 of the slot 14 and ending with an upper conductor ( strap ) 6 in correspondence with the upper wall 40 of the slot 14 , a lower channel 3 formed between the lower conductor ( strap ) 5 and the bottom wall 38 of the slot 14 , an upper channel 4 formed between the upper conductor ( strap ) 6 and the upper wall 40 of the slot 14 , said lower 3 and upper 4 channels serving the passage of a cooling fluid, preferably oil , of the stator 15.

Preferably, the slot 14 comprises a shrinkage and/or a support teeth 7 in correspondence with the bottom wall 38 and/or in correspondence with the upper wall 40 of the slot 14 , to prevent inserting the strap 2 in contact with the bottom wall 38 and/or the upper wall 40 and to leave a free space to form the lower 3 and upper 4 channels ; preferably the bottom wall 38 and the upper wall 40 of the slot 14 have a semi-circular or arched shape .

In the embodiment of the closed-slots stator 15 of the invention, which comprises the side walls 42 of the slot 14 curved or concave , the slot 14 also comprises micro-channels formed in the space between the conductor 2 and the side walls 42 ; said additional fluid ( oil ) passage increases the heat exchange between the cooling fluid and the conductor 2 .

The cooling system with fluid inj ection of the stator 15 with closed slots 14 of the invention comprises a pump 48 , a thermostat 47 and known suitable temperature and flow sensors 49 positioned downline of the electric machine 50 in order to make the cooling fluid flow inside the channels 3 , 4 at a constant temperature and flow .

Thanks to that , the evacuation of the heat in the stator 15 is very ef ficient , since it happens directly in contact with the winding conductors that are the main source of heat dissipation of the electric machine .

The cooling system allows to limit the rise of the temperature of the winding during the functioning of the electric machine , limiting the increase in resistivity of the conductor with temperature , reducing the conduction and proximity losses with equal current , compared to equivalent versions without cooling channels .

Advantageously, the ef ficiency of the electric machine increases considerably and, in the face of lower losses , it is possible to improve performance during continuous operations of the electric motor and to reach higher currents during peak operations . Average power increases , as well as mass power, allowing to obtain lighter machines with equal power compared to equivalent machines without the cooling directed on the windings .

In a preferred embodiment of the invention, the closed-slots stator 15 of the invention comprises a continuous winding comprising at least one strip 11 , 21 , 31 , which in turn comprises a plurality of first sectors 12 connected to each other by a plurality o f second sectors 13 alternating with them, said at least one strip 11 , 21 , 31 being configured to be wound on the first internal stator part 25 , positioning the first sectors 12 of the strip 11 , 21 , 31 in the spaces 27 between the teeth 26 . Preferably the first sectors 12 are parallel , each first sector 12 being connected with at least one end thereof to a second sector 13 , and the winding comprises three strips 11 , 21 , 31 alternating with each other . In a preferred embodiment of the stator 15 with closed slots according to the invention, the second external annular stator part 35 is composed of sectors 45 associated with each other .

Advantageously, the stator 15 with closed slots with cooling system with inj ection of fluid of the invention allows making windings with lower costs , better filling of the slots by the winding, also simpli fying the production process .

In addition, the closed-slot stator with cooling system with fluid inj ection of the invention allows optimi zing the ef ficiency or operation of an electric machine in a desired operating direction .