Patent ID: 6352243
Filing Date: 2002-03-05
Classification: B66D

Abstract:
A chain hoist comprising:a drive shaft transmitting a rotational force to a load sheave; a pressure receive member firmly secured to said drive shaft; a backstop wheel rotating in one direction only relative to said drive shaft; a pressing drive member adapted to be screwed on said drive shaft in a manner allowing its advance and retreat, with said backstop wheel being sandwiched between said pressing drive member and said pressure receive member; an axial fore-end defined on said drive shaft adjacent said pressing drive member; a large-diameter boss projecting from said pressing drive member in the direction toward said axial fore-end; a small-diameter boss projecting from said large-diameter boss in the direction toward said axial fore-end, said small-diameter boss having threaded grooves formed in its peripheral surface; a rotary drive member adapted to be fitted rotatably around said large-diameter boss of said pressing drive member, said rotary drive member facing said pressing drive member in said axial direction; a plurality of lock teeth having a substantially triangular section, said lock teeth being formed on confronting faces of said pressing drive member and said rotary drive member, said lock teeth confronting each other being engaged with each other; a gently sloped face constituting each of said lock teeth, said gently sloped faces confronting each other being pressed against each other when said rotary drive member is rotated relative to said pressing drive member in the winding up direction; a steeply sloped face constituting each of said lock teeth, said steeply sloped faces confronting each other when said rotary member is rotated relative to said pressing drive member in the winding down direction; a first engaging portion formed on the outer periphery of said rotary drive member; a driving wheel adapted to be fitted around the outer periphery of said rotary drive member, said driving wheel having first engaged portion meshing with said first engaging portion of said rotary drive member; a second engaging portion formed on said small-diameter boss that protrudes from said rotary drive member in the direction toward the fore-end when said rotary drive member is fitted around said large-diameter boss; a rotation limit member having a larger external diameter than the internal diameter of said driving wheel, the outer peripheral edge of said rotation limit member serving as a restricting portion for restricting a displacement of said driving wheel in the direction toward said axial fore-end, said rotation limit member having on its inner periphery a second engaged portion that is engaged with said second engaging portion at the fore-end of said large-diameter boss; biasing means fitted around said small-diameter boss at a position closer to said axial fore-end than said rotation limit member, said biasing means providing a biasing force insufficient to cause said lock teeth of said rotary drive member to climb over said steeply sloped faces of said lock teeth of said pressing drive member when said rotary drive member is rotary in the wind-down direction upon the winding-down operation, said biasing means providing a biasing force sufficient to cause said lock teeth of said rotary drive member to climb over said gently sloped faces of said lock teeth of said pressing drive member when an overload is applied to said rotary drive member upon the winding up operation; and a nut adapted to be screwed into said small-diameter boss, for positioning said biasing means relative to said pressing drive member.