Importance

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Abstract

A wrap spring operating mechanism for use in a random start/stop clutch, brake, or combined clutch/brake assembly limits the rate of acceleration or deceleration of the second member relative to the first member when the assembly is engaged. The assembly includes a first member, a second member, and a helical spring wrapped about adjacent portions of the first and second members. An annular control collar is disposed circumferentially about portions of the first and second members. The wrap spring has a first end that is connected to the first member and a second end that is connected to the control collar. An annular armature is connected to the control collar for rotational movement therewith and for relative axial movement. An annular rotor is disposed circumferentially about and connected to the second member. An annular friction ring is disposed within a recess formed in the rotor. The friction ring is formed from a material having a relatively low coefficient of friction, preferably about 0.2 or less under both wet and dry conditions. An electromagnetic coil assembly is provided for selective moving the armature into frictional engagement with the friction ring carried on the rotor to engage the assembly. By forming the friction ring from a non-magnetically permeable material having a relatively low coefficient of friction, the time duration of the frictional engagement of the armature with the friction plate is enlarged. As a result, the rate of acceleration or deceleration of the second member relative to the first member is limited to prevent undesirable impact loads from being generated, particularly when the assembly is operated at high speeds or when relatively large load are placed thereupon.

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First Claim