Passive Compensation of the Temperature Effect on Permanent Magnet Thrust Bearing in Hybrid System

Combining a permanent magnet thrust bearing (PMTB) with mechanical bearings inside a hybrid system can be a good compromise for some applications subject to high axial load. The guidance of the shaft is ensured by the mechanical bearings while those latter are relieved from the axial load by the magnetic bearing. However, as the permanent magnet properties depend on the temperature, this load relieve depends on the operating conditions. This paper describes a compensation system to maintain the force developed by the PMTB constant and independent from the temperature. This system consists in a soft spring placed in series with the static part of the PMTB allowing a variation of the airgap thickness. It is shown that when the stiffness of the soft spring is low enough compared to the equivalent stiffness of the PMTB, it is possible to maintain a constant load relieve for a wide range of operating temperature conditions. Practical implementations based on pressurized bellows are described.