Rotor disk and assembly method

1. A rotor disk for an electric motor comprising:

a shaft hole for receiving a shaft of the electric motor; and

a set of positioning holes around the shaft hole, each configured to receive a positioning pin,

wherein the shaft hole is arranged centrally to the rotor disk, the shaft hole and the set of positioning holes are positioned in the rotor disk such that when the rotor disk is set to a rotated position with respect to another similar rotor disk, and the shaft and the positioning pins are penetrated to respective holes of the two rotor disks, the disks cause a pressing force to the shaft, and

wherein the set of positioning holes form a plane-geometrical shape whose center of weight differs from a center of the shaft hole wherein the shaft hole and the set of positioning holes are arranged asymmetrically with respect to each other; and

wherein the set of positioning holes is arranged asymmetrically with respect to the centrally arranged shaft hole.

2. The rotor disk according to claim 1 , wherein the center of weight of a polygon drawn via the positioning holes deviates from the center of the shaft hole.

3. An electric motor, wherein the electric motor comprises:

a plurality of rotor disks according to claim 2 , wherein at least two of the rotor disks are set to a rotated position with respect to the other rotor disks when the shaft and the positioning pins are mounted to the electric motor such that the rotor disks apply a pressing force to the shaft.

4. The electric motor according to claim 3 , wherein the electric motor comprises:

a shaft having a circular cross-section, wherein a diameter of the cross-section of the shaft is smaller than diameters of the shaft holes in the plurality of the rotor disks when at the same temperature.

5. The rotor disk according to claim 1 , wherein the set of positioning holes and the shaft hole are arranged with respect to each other such that if two similar rotor disks are aligned with each other and one of the disks is rotated 360 degrees divided by the number of positioning holes, at least one of the shaft hole and the positioning holes is only partly overlapping with the respective hole in the other rotor disk.

6. The rotor disk according to claim 1 , wherein the mutually rotated disks are configured to exert substantially opposite pressing forces to the shaft.

7. The rotor disk according to claim 1 , wherein the rotor disk is configured to flex when the shaft is inserted into the shaft hole or when a positioning pin is inserted into the positioning hole.

8. The rotor disk according to claim 1 , wherein the shaft hole is a circle for receiving a shaft having a circular cross-section.

9. An electric motor, wherein the electric motor comprises:

a plurality of rotor disks according to claim 1 , wherein at least two of the rotor disks are set to a rotated position with respect to the other rotor disks when the shaft and the positioning pins are mounted to the electric motor such that the rotor disks apply a pressing force to the shaft.

10. The electric motor according to claim 9 , wherein the electric motor comprises:

a shaft having a circular cross-section, wherein a diameter of the cross-section of the shaft is smaller than diameters of the shaft holes in the plurality of the rotor disks when at the same temperature.

11. An electric motor, wherein the electric motor comprises:

a plurality of rotor disks according to claim 1 , wherein at least two of the rotor disks are set to a rotated position with respect to the other rotor disks when the shaft and the positioning pins are mounted to the electric motor such that the rotor disks apply a pressing force to the shaft.

12. The electric motor according to claim 11 , wherein the electric motor comprises:

a shaft having a circular cross-section, wherein a diameter of the cross-section of the shaft is smaller than diameters of the shaft holes in the plurality of the rotor disks when at the same temperature.

13. A method of mounting a motor shaft to a rotor of an electric motor, comprising:

providing a plurality of rotor disks having a shaft hole for receiving the shaft of the electric motor and a set of positioning holes, each provided for receiving a positioning pin, wherein the shaft hole and the set of positioning holes are positioned in the rotor disk such that there is only one mutual rotation position when the holes of the disks are fully overlapping with each other;

rotating at least some of the rotor disks with respect to each other such that, in the plurality of the rotor disks, one of the shaft holes and the set of the positioning holes are overlapping with each other, and one of the shaft holes and the set of the positioning holes are only partially over-lapping with each other;

inserting first the motor shaft to the shaft hole or the positioning pins into the positioning holes, depending on which of the holes in the disks are overlapping with each other, and

inserting secondly the motor shaft to the shaft hole or the positioning pins to the positioning holes, depending on which of the holes in the disks are only partially overlapping with each other.

14. The method of claim 13 , comprising:

providing a plurality of rotor disks having an eccentrically positioned shaft hole, and arranging a set of positioning holes arranged symmetrically to the rotor disk;

rotating at least some of the rotor disks with respect to each other such that the shaft holes are only partially overlapping with each other and the symmetrically positioned positioning holes are overlapping with each other;

inserting the positioning pins into the positioning holes of the plurality of the rotor disks; and

pressing the motor shaft to the shaft holes of the rotor disks.

15. The method of claim 13 , comprising:

providing a plurality of rotor disks having a centrally positioned shaft hole, and a set of positioning holes arranged at least partially asymmetrically with respect to the centrally arranged shaft hole;

rotating at least some of the rotor disks with respect to each other such that the positioning holes only partially overlap with each other; and

inserting the motor shaft into the shaft holes of the plurality of the rotor disks; and

pressing the positioning pins to the positioning holes of the rotor disks when the motor shaft has been inserted into the shaft holes of the rotor disks.