Rotor structure for a permanent magnet electrical machine
A rotor structure of a permanent magnet electrical machine and a method for manufacture of the rotor structure. The rotor structure has a shaft. An outer surface of the shaft is provided with a permanent magnet. A support collar encircles the permanent magnet. A protective piece is located between the outer surface of the shaft and an inner surface of the support collar and is arranged as an axial mechanical extension for the permanent magnet. The protective piece reduces local maximum values of forces forming between the support collar and the permanent magnet during rotation of the rotor.
1. A rotor structure of a permanent magnet electrical machine, the rotor structure comprising:
a shaft,
a permanent magnet,
a support collar encircling the shaft and the permanent magnet, and
a protective piece located between an outer surface of the shaft and an inner surface of the support collar and arranged as an axial mechanical extension for the permanent magnet,
wherein a mass midpoint of the protective piece is located at a distance from a geometrical rotation axis a structure of the rotor, said protective piece extending in a tangential direction over less than half of an inner circumference of the support collar.
2. The rotor structure according to claim 1 , wherein the permanent magnet is located in a recess on the outer surface of the said shaft.
3. The rotor structure according to claim 2 , wherein a piece comprising magnetically non-conductive material is located next to a surface pointing to the tangential direction of the permanent magnet.
4. The rotor structure according to claim 1 , further comprising:
a sleeve arranged on the outer surface of the shaft, the sleeve comprising magnetically non-conductive material and comprising a through hole for the permanent magnet, and arranged to support the support collar in relation to the shaft.
5. The rotor structure according to claim 1 , wherein the permanent magnet has a radial play between the support collar and the shaft.
6. The rotor structure according to claim 5 , wherein the space making possible the play contains elastic material.
7. The rotor structure according to claim 1 , wherein the rotor structure comprises at least two axially successive sections, each section comprising:
a permanent magnet,
a support collar encircling the shaft and the permanent magnet, and
a protective piece located between the outer surface of the shaft and the inner surface of the support collar and arranged as an axial mechanical extension for the permanent magnet.
8. The rotor structure according to claim 1 , wherein the support collar comprises carbon fiber, wherein fibers of the carbon fiber are substantially oriented in the tangential direction.
9. The rotor structure according to claim 1 , wherein the support collar comprises titanium.
10. A permanent magnet electrical machine, comprising:
a rotor, comprising
a shaft fitted to a frame of the electrical machine with bearings,
a permanent magnet,
a support collar encircling the shaft and the permanent magnet, and
a protective piece located between an outer surface of the shaft and the inner surface of the support collar and arranged as an axial mechanical extension for the permanent magnet,
wherein a mass midpoint of the protective piece is located at a distance from a geometrical rotation axis of the rotor, said protective piece extending in a tangential direction over less than half of an inner circumference of the support collar.
11. A method for manufacture of a permanent magnet electrical machine, the method comprising:
installing a protective piece so that the protective piece forms an axial mechanical extension for an permanent magnet in the rotor and wherein a mass midpoint of the protective piece remains at a distance from a geometrical rotation axis of the rotor, said protective piece extending in a tangential direction over less than half of an inner circumference of the support collar, and
installing a support collar to encircle the rotor shaft, the permanent magnet and the protective piece so that the protective piece remains between an outer surface of the shaft and an inner surface of the support collar.