Electrical machines are well known in the prior art. For instance, direct current motors excited permanent-magnetically are known, which can be commutated electronically or mechanically. Two types can be distinguished, namely one in which the permanent magnets are located on the stator, and another in which the permanent magnets are mounted on the rotor. The commutated magnetic field between the permanent magnet and the coils located on the other component bring about the torque on the rotor shaft.
For securing the permanent ring magnet on a rotor body of the rotor shaft, it is known for instance from European Patent Disclosure EP 0 872 945 A1 to use an adhesive bond. Because of different temperature expansions of the different materials comprising the magnet, adhesive and rotor body, and because of manufacturing variations, and because of the spacing between the magnet and the rotor shaft/rotor body required when an adhesive is used, major material stresses on the individual materials (magnet, adhesive, shaft) occur at the joining faces. In operation of the electrical machine, major temperature differences can additionally occur, which because of the different coefficients of expansion of the materials lead to cracks and even to the point of material breakage, so that transmission of a torque from the magnet to the rotor shaft is no longer possible. The mechanical properties of the adhesive furthermore become poorer as the temperature increases, and as a consequence the magnet is no longer fixed to the rotor shaft solidly enough.
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USPTO Backgrounds