Method to construct an electric machine having a stator winding with rigid bars

1. A method to construct an electric machine ( 1 ), which comprises:

a stator ( 5 ) comprising a magnetic core ( 6 ) longitudinally crossed by a plurality of stator slots ( 7 ); and

a stator winding ( 8 ) having a number of phases and comprising a series of rigid bars ( 9 ), which are “U”-shaped and are inserted through the stator slots ( 7 ) defining an entry side ( 12 ), in which the cusps ( 11 ) of the “U”-shaped bars ( 9 ) are placed, and an exit side ( 13 ), in which the legs ( 10 ) of the “U”-shaped bars ( 9 ) are placed;

the construction method comprises the steps of:

twisting the legs ( 10 ) of the “U”-shaped bars ( 9 ) coming out from the exit side ( 13 ) of the magnetic core ( 6 ) through relative double folds, each of which comprises an internal fold ( 15 ) in one direction and an external fold ( 16 ) in the opposite direction;

electrically connecting to one another the ends of the legs ( 10 ) of the “U”-shaped bars ( 9 ) so as to form the electrical paths of the stator winding ( 8 );

electrically connecting the ends of at least two non-adjacent legs ( 10 ) by means of a connection bridge ( 18 ; 28 ; 30 ; 32 ; 34 ), which is made of a flat plate arranged perpendicular to the central axis ( 3 ) of rotation and has, for each leg ( 10 ), a corresponding “U”-shaped seat ( 19 ), which is suited to receive the end of the leg ( 10 ) itself;

initially manufacturing the seats ( 19 ) of the connection bridge ( 18 ; 28 ; 30 ; 32 ; 34 ) with a size that is larger, beyond the tolerance needed to simply insert the ends of the legs ( 10 ), than the ends of the corresponding legs ( 10 );

inserting into the seats ( 19 ) of the connection bridge ( 18 ; 28 ; 30 ; 32 ; 34 ) the ends of the corresponding legs ( 10 ), so that the end of each leg ( 10 ) is “loose” inside the corresponding seat ( 19 ); and

locally and plastically deforming the connection bridge ( 18 ; 28 ; 30 ; 32 ; 34 ) so as to tighten the seats ( 19 ) of the connection bridge ( 18 ; 28 ; 30 ; 32 ; 34 ) around the ends of the corresponding legs ( 10 ).

2. A construction method according to claim 1 , wherein:

each seat ( 19 ) is delimited on three sides by two lateral walls and by a rear wall which is interposed between the two lateral walls;

each seat ( 19 ) is open on the fourth side opposite the rear wall.

3. A construction method according to claim 2 , wherein:

at first the two lateral walls of each seat ( 19 ) are not parallel to one another and each forms a corresponding obtuse angle with the rear wall; and

once the end of the leg ( 10 ) has been inserted into the seat ( 19 ), the seat ( 19 ) is caused to shrink, thus bringing the two lateral walls closer to each other and therefore the two lateral walls become parallel to each other and each forms a corresponding right angle with the rear wall.

4. A construction method according to claim 1 , and comprising the further step of welding the connection bridge ( 18 ; 28 ; 30 ; 32 ; 34 ) to the ends of the corresponding legs ( 10 ) after the step of locally and plastically deforming the connection bridge ( 18 ; 28 ; 30 ; 32 ; 34 ).

5. A construction method according to claim 1 , wherein:

the connection bridge ( 18 ; 28 ; 30 ; 32 ; 34 ) is made up of a central body with a substantially constant cross-section and of a series of appendages, which project From the central body and are perpendicular to the central body itself; and

each seat ( 19 ) is delimited, on the rear side, by the central body and is laterally delimited by a pair of appendages that are arranged one in front of the other.

6. A construction method according to claim 5 , wherein, in each seat ( 19 ), an appendage has a linear shape in its plan view and the other appendage is “L”-shaped in its plan view, so as to embrace the end of the corresponding leg ( 10 ) on two sides.

7. A construction method according to claim 6 , wherein the appendage with the linear shape initially forms a right angle with the central body and the “L”-shaped appendage initially forms an obtuse angle with the central body.

8. A construction method according to claim 5 , wherein an appendage initially forms a right angle with the central body and the other appendage initially forms an obtuse angle with the central body.

9. A construction method according to claim 1 and comprising the further steps of:

arranging a set of first connection bridges ( 18 ), which are coplanar to one another, at a first axial height; and

arranging a set of second connection bridges ( 28 ), which are coplanar to one another, at a second axial height that is different from the first axial height, so that the second connection bridges ( 28 ) are above the first connection bridges ( 18 ).

10. A construction method according to claim 9 , wherein:

each first connection bridge ( 18 ) has two seats ( 19 ) to connect the ends of two corresponding legs ( 10 ) to one another; and

each second connection bridge ( 28 ) has three seats ( 19 ) to connect the ends of three corresponding legs ( 10 ) to one another.