| 摘要 |
A pulley comprising a first pulley wheel (12) and a second pulley wheel (14) and a ratchet acting between the two pulley wheels (12,14). When substantially equal force is applied to each pulley wheel in use on a rope tail side causing the pulley wheels to rotate, a low gear ratio is achieved through a rope, chain or the like acting on a load through a block (22). When one pulley wheel is prevented from rotating and a force is applied to the other pulley wheel in use on a rope tail side causing it to rotate, then a higher gear ratio is achieved through a rope or chain or the like acting on a load through a block. When force is applied to the first wheel on a rope tail side and the second pulley wheel is allowed to rotate, then a still higher ratio is achieved in use through a rope, chain or the like acting on a load through a block. In another embodiment, the pulley comprises a first pulley wheel, a second pulley wheel and means to prevent relative rotation of the pulley wheels in one direction, the pulley wheels being able to rotate relative to each other in the other direction. In another embodiment, the pulley comprises a first pulley wheel, a second pulley wheel and means acting between the pulley wheels such that, a force acting to rotate the first pulley wheel in a first direction imparts a corresponding force to rotate the second pulley wheel in a second, opposite direction. |
