Shaft-coupling device preventable from over-torque transmission

Claim 1

A shaft-coupling device preventable from over-torque transmission, comprising; a driving shaft having a co-axial cylindrical pipe end, a driven shaft having a co-axial cylinder end with a smaller out-side diameter than the inner side diameter of said driving shaft pipe end, said driven shaft cylinder end being inserted and coupled rotatably to said driving shaft pipe end, a wedge ring having an inclined side wall, a bolt having a head of greater diameter and with its circumferential wall inclined, at least one steel ball inserted between said driving shaft pipe end and driven shaft cylinder end and being urged radially outwardly by the wedge ring and bolt head, with said wedge ring being urged toward the ball by a spring placed between the wedge ring and a nut engaging a screwthreaded end of the bolt, wherein said wedge ring and said bolt are supported rotatably in contact with the balls inside said cylinder end, whereby, in a state of normal-torque transmission, said steel ball is so positioned as to engage both said driving shaft pipe enD and said driven shaft cylinder end, such that while said driven shaft is over-loaded, said steel ball is forced to push said wedge ring apart from the inclined wall of the bolt and having another position such as to engage either one of said driving shaft pipe end or said driven shaft cylinder end.