| 摘要 |
A rotary electrical machine comprising a stator (10) and at least one rotor (12) having a plurality of permanent magnets (14) The rotor consists of a rotor disc, at the outer edge of which the permanent magnets are mounted. The rotor disc (12) is provided with airgap varying means (19) which are angled towards the stator (10) and mounted on the rotor hub (24) for rotation therewith. When the rotor is stationary, the airgap (30) between the magnets (14) and the stator (10) is at a minimum. In operation, as the speed of rotation of the rotor (12) increases, a centrifugal force is generated which acts to bend the airgap varying means (19) and, therefore, the rotor disc (12) back, away from the stator (10), thereby drawing the magnets (14) away from the stator and increasing the size of the airgap (30). The increase in size of the airgap results in a corresponding decrease in flux and therefore a decrease in the maximum output voltage for that rotor speed. In this way, the output voltage of the machine is kept substantially constant. A stationary iron ring (32) may be provided on the stator (10) to assist in drawing away flux as the size of the airgap is increased.
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