Hoist

Abstract

A hoist includes a shaft driven by external force, a driving shaft connected to the shaft, a reduction gear train for transmitting rotation of the driving shaft to a load sheave, a mechanical brake assembly in the reduction gear train, and an overload safety device having a clutch mechanism capable of transmitting torque larger in driving said load sheave in a winding-off direction than that in a winding-up direction. According to the invention, the clutch mechanism comprises a disc-like driving member, a disc-like driven member, surfaces of these members facing to each other being formed with a plurality of recesses which are arranged in circles on the surfaces of these members and in opposition to each other, slide elements each accommodated in each set of the opposite recesses respectively formed in these members, and resilient urging means for urging the slide elements between the driving and driven members, any one of each set of the recesses having a gentle slope surface facilitating each the slide element to ride thereon and slip when driving the load sheave in the winding-up direction. The hoist according to the invention is capable of automatically preventing the lifting, lowering or dragging of a load under overload condition, and enabling the once lifted load to be securely lowered regardless of its light or heavy weight, and is simple in construction, easy to assemble and adjust and suitable for mass-production.