Model AO Automatic Torque Limiter
Bi-Directional · Single Position · Automatic Reset
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A CABAT Model AO Overload Clutch installed in the drive line of
rotating machinery provides a torsionally-rigid driving connection until
a torque overload occurs, at which time the clutch will instantly disengage,
thus
protecting the drive train components from the torque overload. After
stopping the drive and removing the overload, restarting the drive (jogging
the motor
or manually rotating input or output) will cause the clutch to re-engage
automatically in the original angular input/output relationship.
The model AO design incorporates a time-proven ball/detent type mechanism operating under direct spring pressure to accurately and consistently respond to torque overloads and instantly release. The multiple balls are carried in precision thru-bores in the clutch hub and "squeezed" between the detents in output rotor and the pressure plate by direct spring pressure. Thus all axial thrust and reaction forces are produced and absorbed by the axial clutch springs directly, without transferring these forces to the clutch hub or the shaft.
When an overload occurs, the transmitted torque forces the balls out of their detents, pushing the spring-loaded pressure plate back until the balls roll out of their detents. Further rotation causes the balls to roll between the output flange face and the pressure plate. During this phase the clutch torque drops to about 5% of the original engaged torque.
The multiple ball/detent "sets" are placed angularly and radially around the clutch hub flange and output flange so as to permit engagement in only one angular position, called single-position re-set which maintains "timing" of machine members. When the released clutch has rotated (relatively) one revolution, the ball/detents reach their single re-engagement position and the constant acting spring pressure tries to force the balls into their mating detents. Depending on the relative rpm, the spring force, and the angular momentum of the rotating drive members, the torque forces generated may again force the balls out of their detents and the cycle repeats until either the overload is removed, and/or the rotation is stopped. This repeating re-set action can produce substantial torsional "clatter" depending on the operation rpm and the clutch torque.
To minimize these effects and to prolong clutch life (1) the operating speed should not exceed 500 rpm, and (2) the rotation should be stopped as soon as possible after the clutch releases. This can be accomplished automatically by use of the switchplate which extends when the clutch releases and retracts when the clutch re-engages. Used in conjunction with a mechanical or proximity limit switch the motor can be switched off or other signaling means activated.
The clutch torque springs are carried on precision shoulder bolts which provides simple quick and easy torque adjustment. The springs should be tightened as evenly as practical, which can be done most easily by tightening the shoulder screws until they "bottom" and then backing them out an equal amount such as 1, 3/4, 1/2 or 1/4 turn. Several torque ranges are offered for each clutch size, and if necessary, springs can easily be changed without clutch removal or disassembly.
This bi-directional clutch can be installed in many different arrangements, keeping in mind that it should be located as near the "torque-sensitive" driven members as possible to provide maximum protection. The clutch is mounted on the shaft and when positioned, is locked in place by the oversize double set screws provided in the clutch hub. Access holes are provided in the clutch body outer diameter. Driven members, plate sprockets, pulleys, or gears can be mounted directly onto the clutch output flange utilizing pilot diameter C and mounting holes M or O. A built-in bearing is provided between the clutch output flange and the hub.
Once properly installed and adjusted, these clutches under normal operating conditions will require minimum maintenance. They are factory lubricated with high grade lubricants, which will not deteriorate in service. The design is simple and rugged, using alloy steel components which have been treated for rust protection. With proper use of limit switches or other drive stopping means at overload, these clutches will provide long, satisfactory service.
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