Lever hoist with overload preventing device

A lever hoist with an overload preventing device comprising:

• a drive shaft for transmitting rotating force to a load sheave;
• a pressed member fixed to the drive shaft;
• a reverse rotation preventing ring which is rotated in only one direction with respect to the drive shaft;
• a pressing member screwed to the drive shaft in such a manner as to freely advance or retreat, and presses the pressed member via the reverse rotation preventing ring;
• a large-diameter boss projecting from the pressing member toward an axial tip;
• a small-diameter boss projecting from the large-diameter boss toward the axial tip and having a screw groove formed at the circumferential surface thereof;
• a rotation drive member rotatably fitted to the large-diameter boss of the pressing member in such a manner as to face the pressing member in the axial direction and having a drive tooth on the outer periphery thereof;
• a plurality of locking teeth, each having a triangular cross section, which are formed at respective circumferential surfaces facing each other, of the pressing member and the rotation drive member, so as to mesh with each other;
• a moderately inclined surface defining the locking tooth, for pressing the pressing member when the rotation drive member is rotated in a hoisting-up direction;
• a sharply inclined surface defining the locking tooth, for pressing the pressing member when the rotation drive member is rotated in a hoisting-down direction;
• an engaging portion formed at the projecting portion of the large-diameter boss projecting toward the tip beyond the rotation drive member when the rotation drive member is fitted to the large-diameter boss;
• a rotation limiting member having an outer diameter greater than the inner diameter of the rotation drive member, for restricting, at the outer peripheral edge thereof, movement toward the axial tip of the rotation drive member, and including, at the inner circumference thereof, an engaged portion to be engaged with the engaging portion at the tip of the large-diameter boss so as to inhibit relative rotation in a circumferential direction;
• urging means fitted to the small-diameter boss nearer the axial tip than the rotation limiting member, and having urging force such that it cannot ride over the sharply inclined surface of the locking tooth when the rotation drive member is rotated in the hoisting-down direction during a hoisting-down operation while it can ride over the moderately inclined surface of the locking tooth when an overload is exerted on the rotation drive member during a hoisting-up operation;
• and
• a nut screwed into the small-diameter boss, for positioning the urging means with respect to the pressing member.