| 摘要 |
PURPOSE:To realize compact structure by disengaging a clutch for coupling between a parking brake and drive means through a release spring made of shape memory alloy while controlling heating of said spring. CONSTITUTION:A pulley 23 to be wound with a wire 14b coupled to a parking brake and a rotary motor 21 for functioning/disabling the parking brake are coupled/interrupted through clutch members 22d, 23a. Upon fault of motor 21 under operating condition of parking brake through coupling of clutch members 22d, 23a, the parking brake is never released automatically. Here, power is fed to release spring 25 to heat it. Since said spring 25 is made of shape memory alloy, spring force is increased upon heating to setting temperature. Consequently, the clutch member 23a is pushed up through the shaft 22a to be uncoupled thus to release braking.
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