Isolation device with selected angle between spring stop and damping member

An isolation device for engagement between an endless drive member for an engine and a shaft of a component in operative engagement with the endless drive member, comprising:

• a hub that is mountable to the shaft of the component;
• a pulley that is rotatable relative to the hub and positioned for engagement with the endless drive member;
• an isolation spring that is a helical torsion spring that is positioned to transfer torque along a torque path between the hub and the pulley, wherein the isolation spring has a first spring end positioned to engage a first spring end engagement feature along the torque path, a second spring end positioned to engage a first spring end engagement feature along the torque path, and a plurality of helical coils between the first and second spring ends;
• and
• a damping member that is fixed rotationally relative to one of the hub and the pulley and is engageable frictionally with the other of the hub and the pulley and is positioned radially between the isolation spring and the other of the hub and the pulley, wherein the damping member has a first angular end and a second angular end and has a selected angular length between the first and second angular ends,
• wherein torque transmission through the isolation spring below a selected non-zero torque, irrespective of hub load on the pulley, drives a change in radius of the helical coils that is sufficiently small that the isolation spring avoids applying a radial force to press the damping member against said other of the hub and the pulley, and
• wherein torque transmission through the isolation spring above the selected non-zero torque, irrespective of hub load on the pulley, drives a change in radius of the helical coils that is sufficiently large that the isolation spring applies a radial force to press the damping member against said other of the hub and the pulley so as to generate frictional damping,
• wherein, as torque transmission through the isolation spring increases, irrespective of hub load on the pulley, beyond the selected non-zero torque, the radial force to press the damping member against said other of the hub and the pulley increases, so as to generate increasing frictional damping.