Angle of Twist for Sprag Clutch Applications

In a sprag clutch, sprags do not go from freewheeling to fully engaged instantaneously. When the sprags are freewheeling, they are still in contact with the mating surfaces, but that contact point is outside the engagement curve. As the relative rotation changes, the sprags start to rotate and move the contact point into the engagement zone.

Once in that zone, elastic deformation starts to take place between the sprag and mating surface, and torque is transmitted. Depending on how much torque is applied, the sprags will continue to rotate until an equilibrium is achieved between the torque transmitted and the elastic deformation and pressure between the sprag and mating surface. That means:

• If the torque is low, the sprags will rotate less and the contact point will be lower on the engagement curve.
• If the torque is high, it will take more elastic deformation to reach equilibrium so the sprags will rotate more and the contact point will be higher on the engagement curve.