Methods of manufacturing rotors having interfering sintered magnets and carbon filament sheaths for electric motors
A method of manufacturing an electric-motor rotor may include providing a magnet of sintered magnetic material, the magnet having a first diameter; providing a sheath of composite material, the sheath having an inner diameter smaller than the first diameter; reducing the first diameter to a second diameter; fitting the sheath onto the magnet when the magnet has the second diameter; and letting the magnet with the sheath fitted thereon to interfere, allowing the sheath to exert inward pressure on the magnet. An electric-motor rotor may include a magnet of sintered magnetic material, the magnet having a first diameter; and a sheath of composite material, the sheath having an inner diameter smaller than the first diameter. The sheath may be associated with the magnet in such a way that the magnet with the sheath fitted thereon interfere so that the sheath exerts inward pressure on the magnet.
1. A method of manufacturing a rotor for an electric motor, the method comprising:
providing a magnet of sintered magnetic material, the magnet having a first diameter;
forming a radial holding sheath of composite material, the forming including winding at least one carbon filament around a chuck to form a wound carbon filament arrangement that is fixed in position by a layer of resin and has an inner diameter that is smaller than the first diameter;
reducing the first diameter of the magnet to a second diameter;
fitting the sheath onto the magnet concurrently with the magnet having the second diameter and the sheath being at room temperature; and
letting the magnet with the sheath fitted thereon to interfere, thus allowing the sheath to exert inward pressure on the magnet.
2. The method of claim 1 , wherein the reducing the first diameter of the magnet comprises:
lowering a temperature of the magnet.
3. The method of claim 2 , wherein the lowering the temperature of the magnet comprises:
dipping the magnet into fluid at low temperature.
4. The method of claim 3 , wherein the low temperature is a temperature lower than about −120° C.
5. The method of claim 3 , wherein the fluid is liquid nitrogen.
6. The method of claim 3 , wherein the low temperature is a temperature lower than −120° C.
7. The method of claim 3 , wherein the low temperature is a temperature lower than −150° C.
8. The method of claim 3 , wherein the fluid comprises liquid nitrogen.
9. The method of claim 1 , wherein the fitting the sheath onto the magnet is carried out substantially without mechanical interference.
10. The method of claim 1 , wherein the letting the magnet with the sheath fitted thereon to interfere comprises:
heating the magnet and the sheath fitted thereon at room temperature.
11. The method of claim 1 , wherein the providing the radial holding sheath of the composite material comprises:
forming the sheath on a chuck and taking the sheath off the chuck.
12. The method of claim 1 , wherein the reducing the first diameter of the magnet comprises:
lowering a temperature of the magnet using fluid at low temperature.
13. The method of claim 12 , wherein the low temperature is a temperature lower than −120° C.
14. The method of claim 12 , wherein the low temperature is a temperature lower than −150° C.
15. The method of claim 12 , wherein the fluid comprises liquid nitrogen.
16. The method of claim 1 , wherein the fitting the sheath onto the magnet is carried out without mechanical interference.
17. The method of claim 1 , wherein the fitting the sheath onto the magnet is carried out with very low interference.
18. The method of claim 1 , wherein the letting the magnet with the sheath fitted thereon to interfere comprises:
heating the magnet and the sheath fitted thereon to room temperature.