Axial-flux electric machine with winding rotor and method for the production thereof

1. An axial-flux electric machine (M) with a winding rotor comprising a stator section (PS) and a rotor section (PR), which both develop around a rotation axis (X) of the electric machine (M), the rotor section (PR) comprising a rotor ( 1 ), which, in turn, comprises:

a rotor core ( 2 ) with a toroidal shape, which develops around the axis (X) and has at least one receiving surface ( 5 ) with an annular shape;

a plurality of teeth ( 4 ), which are arranged in contact with said receiving surface ( 5 ) and extend away from the receiving surface ( 5 ) along said axis (X), each one of said teeth ( 4 ) having a first tangential surface ( 4 c ) facing the axis (X) and a second tangential surface ( 4 d ) opposite to said first tangential surface ( 4 c );

a plurality of windings ( 3 ), which are angularly distributed around said axis (X) and cooperate with said rotor core ( 2 ) and said teeth ( 4 ) so as to concatenate a magnetic flux flowing through the rotor core ( 2 ) and the teeth ( 4 ),

characterised in that at least one of said teeth ( 4 ) has, on at least one of said tangential surfaces ( 4 c , 4 d ), a shaped profile defining at least one holding surface ( 12 ), which faces away from the toroidal rotor core ( 2 ), and in that said rotor ( 1 ) has a resin matrix that binds together said toroidal rotor core ( 2 ) and said teeth ( 4 ), wherein the resin matrix engages together said holding surface ( 12 ) and said toroidal rotor core ( 2 ) to lock the tooth ( 4 ) on the toroidal rotor core ( 2 ).

2. A machine (M) according to claim 1 , characterised in that, in said rotor ( 1 ), said holding surface ( 12 ) is defined by a step ( 13 ) of said shaped profile ( 13 ) and is substantially parallel to said receiving surface ( 5 ) of the toroidal rotor core ( 2 ).

3. A machine (M) according to claim 1 , wherein said holding surface ( 12 ) is defined at least on said first tangential surface ( 4 c ) of at least one tooth ( 4 ).

4. A machine (M) according to claim 1 , wherein said at least one holding surface ( 12 ) is defined by each one of said teeth ( 4 ).

5. A machine (M) according to claim 1 , wherein said holding surface ( 12 ) is defined at least on said second tangential surface ( 4 d ) of said at least one tooth ( 4 ), and wherein the rotor ( 1 ) comprises an outer casing ( 11 ), which shaped so as to embrace said second tangential surfaces ( 4 d ) of the teeth ( 4 ) and has at least one locking portion, which can be engaged with said holding surface ( 12 ) so as to keep the tooth ( 4 ) pressed against said toroidal rotor core ( 2 ).

6. A machine (M) according to claim 5 , wherein said at least one holding surface ( 12 ) is defined by each one of said teeth ( 4 ), and wherein the locking portion of the casing ( 11 ) extends in a circumferential manner along an entire angular length developing around the axis (X) and can be engaged with said holding surfaces ( 12 ) of the teeth ( 4 ) so as to keep the teeth ( 4 ) pressed against said toroidal rotor core ( 2 ).

7. A machine (M) according to claim 1 , wherein said teeth ( 4 ) are angularly distributed around said axis (X) so as to define, between two successive teeth ( 4 ), a respective slot ( 14 ), and wherein each one of said windings ( 3 ) is at least partially housed inside one of said slots ( 14 ) and fitted onto the toroidal rotor core ( 2 ).

8. A machine (M) according to claim 1 , wherein each one of said windings ( 3 ) is fitted onto a respective tooth ( 4 ).

9. A machine (M) according to claim 1 , wherein each tooth ( 4 ) has, furthermore, a base wall ( 4 a ) resting on the receiving surface ( 5 ) of the toroidal rotor core ( 2 ) and a top wall ( 4 b ) opposite to said base wall ( 4 a ), wherein said top wall ( 4 b ) has an outer flat surface ( 10 ), which is parallel to said receiving surface ( 5 ) of the toroidal rotor core ( 2 ) and laterally abuts on the corresponding top walls ( 4 b ) of the adjacent teeth ( 4 ).

10. A machine (M) according to claim 1 , wherein each tooth ( 4 ) has, furthermore, a base wall ( 4 a ) resting on the receiving surface ( 5 ) of the toroidal rotor core ( 2 ) and a top wall ( 4 b ) opposite to said base wall ( 4 a ), wherein said top wall ( 4 b ) as an outer flat surface ( 10 ), which is parallel to said receiving surface ( 5 ) of the toroidal rotor core ( 2 ) and is laterally spaced apart from the corresponding top walls ( 4 b ) of the adjacent teeth ( 4 ), so to as to define a respective gap, said rotor ( 1 ) comprising, furthermore, at least one fixing ring made of a ferromagnetic material, which is rigidly connected to the top walls ( 4 b ) of the teeth ( 4 ) so as to establish an electric and magnetic continuity among the teeth ( 4 ).

11. A machine (M) according to claim 1 , wherein said toroidal rotor core ( 2 ) has a first and a second receiving surfaces ( 5 ) with an annular shape, which are opposite to one another and substantially perpendicular to said axis (X), and wherein said plurality of teeth ( 4 ) are divided into a first series of teeth ( 4 ) applied to said first receiving surface ( 5 ) and extending away from the first receiving surface ( 5 ) along said axis (X) and a second series of teeth ( 4 ) applied to said second receiving surface ( 5 ) and extending away from the second receiving surface ( 5 ) along said axis (X), at least one tooth ( 4 ) of each series having said holding surface ( 12 ).

12. A method to produce an axial-flux electric machine (M) comprising the following steps: manufacturing a stator section (PS); manufacturing a rotor section (PR); arranging the rotor section (PR) and the stator section (PS) in a predetermined relative position along a rotation axis (X) of the electric machine (M); the step of manufacturing the rotor section (PR) comprising the step of manufacturing a rotor ( 1 ), which, in turn, comprises the sub-steps of:

providing a rotor core ( 2 ) made of a ferromagnetic material, which develops around a circular line and has at least one receiving surface ( 5 ) lying on said circular line;

providing a plurality of teeth ( 4 ) made of a ferromagnetic material, each tooth ( 4 ) having a base wall ( 4 a ), which can be engaged with said receiving surface ( 5 ), a top wall ( 4 b ), which is opposite to the base wall ( 4 a ), and at least two tangential walls ( 4 c , 4 d ), which are opposite to one another and are delimited by said base wall ( 4 a ) and top wall ( 4 b ), and wherein at least one of said teeth ( 4 ) has, on at least one of said tangential surfaces ( 4 c , 4 d ), a shaped profile defining at least one holding surface ( 12 ) facing away from the base wall ( 4 a );

providing a plurality of windings ( 3 );

applying the teeth ( 4 ) to the rotor core ( 2 ) so that the base wall ( 4 a ) of each tooth ( 4 ) is arranged so as to simply rest on said receiving surface ( 5 );

applying the windings ( 3 ) to the rotor core ( 2 ) so that the windings ( 3 ) cooperate with the rotor core ( 2 ) and with the teeth ( 4 ) in order to concatenate with a magnetic flux flowing through the rotor core ( 2 ) and the teeth ( 4 );

after the teeth ( 4 ) have been applied to the rotor core ( 2 ), impregnating the rotor core ( 2 ) and the teeth ( 4 ) with a resin matrix, so that the resin sticks to the holding surface ( 12 ), thus locking the teeth ( 4 ) to the rotor core ( 2 ).

13. A method according to claim 12 , wherein between the sub-step of applying the teeth ( 4 ) to the rotor core ( 2 ) and the sub-step of impregnating the rotor core ( 2 ) and the teeth ( 4 ) with a resin matrix there is interposed the sub-step of securing the teeth ( 4 ) to the rotor core ( 2 ) by inserting the rotor core ( 2 ) and the teeth ( 4 ) applied thereto into a die.

14. A method according to claim 12 , wherein the sub-step of providing a rotor core ( 2 ) made of a ferromagnetic material is performed by providing two half-rings ( 2 a , 2 b ) made of a ferromagnetic material, and wherein said sub-step of applying the windings ( 3 ) to the rotor core ( 2 ) is performed by fitting said windings ( 2 ) onto the respective half-ring ( 2 a , 2 b ), said sub-step of applying the windings ( 3 ) to the rotor core ( 2 ) is performed before the step of applying the teeth ( 4 ) to the half-rings ( 2 a , 2 b ); said method comprising, furthermore, the sub-step of joining said half-rings ( 2 a , 2 b ) so as to obtain the entire toroidal rotor core ( 2 ).

15. A method according to claim 12 , wherein the sub-step of providing a rotor core ( 2 ) is performed by providing a single rotor core ( 2 ) with a toroidal shape made of a ferromagnetic material, and wherein the sub-steps of applying the teeth ( 4 ) to the rotor core ( 2 ) and applying the windings ( 3 ) to the rotor core ( 2 ) are performed by fitting each winding ( 3 ) onto a respective tooth ( 4 ) and by subsequently applying the tooth ( 4 ) to the rotor core ( 2 ) by laying the base wall ( 4 a ) of the tooth ( 4 ) onto the receiving surface ( 5 ) of the rotor core ( 2 ).

16. A method according to claim 12 , wherein the sub-step of applying the teeth ( 4 ) to the rotor core ( 2 ) is preceded by the sub-step of mutually connecting at least a sub-set of said teeth ( 4 ) by fixing the top wall ( 4 b ) of said teeth ( 4 ) to a fixing ring made of a ferromagnetic material.

17. A method according to claim 12 , wherein the step of manufacturing the rotor ( 1 ) comprises the sub-step of coupling a casing ( 11 ) with an annular shape to the outside of the toroidal rotor core ( 2 ), the teeth ( 4 ) and the windings ( 3 ), said casing ( 11 ) having at least one locking portion, which can be engaged with said holding surface ( 12 ) of said at least one tooth ( 4 ) so as to keep the tooth ( 4 ) pressed against said toroidal rotor core ( 2 ).