| 摘要 |
PURPOSE:To prevent a brush from flowing an excess current by operating a retainer when the excess current flows to the brush and holding and restricting the brush. CONSTITUTION:Since a brush 3 is released from a retainer 9 in an allowable range of a brush energizing current, it is pressed by a pressing spring 6, and slidably contacted with a slip ring 5. When the excess current which exceeds the allowable limit is flowed to the brush 3, the brush sliding surface temperature rises, and heat is transmitted to the retainer 9. Since the portion for holding the brush 3 of the retainer 9 and the vicinity are formed of a shape memory metal, the retainer 9 operates when it reaches the temperature stored in advance, bends and deflects to hold the side of the brush 3 to suppress the slip ring 6 from pressing the brush pressing force to the side of the ring 5 of the ring 6. The brush 3 is gradually worn to decrease the pressure of the brush. |
