Spring clutch

Abstract

A spring clutch is provided for which durability is improved by preventing a clutch spring from breaking due to fatigue. A cylindrical clutch spring made from a wire having a square section is mounted between a pulley and a pulley hub mounted in the pulley. An end of the clutch spring is coupled to the pulley hub. A clutch surface is formed on the inner periphery of the pulley and is formed with a large-diameter recess at a position opposite to the end portion of the clutch spring including the torque transmission end. When the pulley rotates in one direction, the clutch spring expands. At this time, the end portion of the clutch spring including the torque transmission end expands in the large-diameter recess, thus relaxing sharp torque produced in the clutch. This prevents local stress concentration on the clutch spring and breakage of the clutch spring and improves the durability of the clutch.

1 . A spring clutch comprising an input member having a cylindrical clutch surface on its inner periphery, an output member mounted in said input member so as to be rotatable relative to said input member, and a cylindrical clutch spring mounted between said input member and said output member and including a torque transmission end through which torque is transmitted to said output member, wherein when said input member rotates in one direction, said clutch spring radially expands by contact with said clutch surface, thereby transmitting torque from said input member to said output member, and when the speed of said output member exceeds the speed of said input member, said clutch spring is radially compressed, thereby cutting off the transmission of torque from said input member to said output member, and wherein said clutch spring has at least one small-diameter portion which are not pressed against said clutch surface when said clutch spring radially expands. 
     
     
         2 . The spring clutch of  claim 2  wherein said small-diameter portion is formed only at an end portion of said clutch spring including said torque transmission end.