Torque Limiters and Slip Clutches

Torque limiters and slip clutches automatically slip or disengage the clutch at a predetermined torque. A variety of torque limiters and slip clutches are available. A unidirectional clutch often used as a safety mechanism.  With an overrunning clutch, the drive element can stop, and the load is allowed to wind down freely. Backstop clutches are freewheeling clutches that transmit torque in one direction only; they are specifically used for preventing drives from "backing up" or driven systems such as inclined conveyors from going down. Freewheeling clutches are unidirectional torque transmitters that spin freely in the direction opposite the intended drive rotation.

Selecting torque limiters and slip clutches requires an analysis of performance specifications such as torque rating, rotary power, and rotational speed. There are several choices for clutch engagement. Noncontact technologies use magnetic fields and eddy currents. Friction clutch engagement uses the friction between contact surfaces to transmit power. This is the most common configuration. Toothed clutch engagement uses toothed contact surfaces to transmit power without slipping. Although toothed clutches do not generate heat, they can be engaged only when stopped at slow speeds (< 20 rpm). Wrap spring engagement systems are torque limiters and slip clutches in which torque is transmitted from input to output by a coiled spring that wraps around the output element.  The clutch is disengaged when the spring is uncoiled via a control tang at its end.

With oil shear torque limiters and slip clutches, drive engagement is achieved via the viscous shear of transmission fluid between the clutch plates. In plate/disc systems, torque level is controlled by compression springs that force plates together. Ball detent is a slip mechanism in which, upon overload, balls ride up out of their seats and overcome springs or air pressure engagement. Roller detent systems use rollers, held in place by springs, which wedge between inner and outer races to engage clutch. Pawl detent clutch slip mechanisms are those in which, upon overload, a pawl overcomes spring or air pressure engagement and rotates out of its detent. Sprag engagement systems use steel wedges that tip in one direction to wedge between inner and outer races. These torque limiters and slip clutches can be configured with either the inner or outer race as the input or output. Too much torque makes the sprags tip too much and contact is no longer held.  Sprag clutches can often transmit more torque than other designs of slip or overrunning clutches.

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Part Numbers for Torque Limiters and Slip Clutches