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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.

Sprag clutch angle of twist diagram indicating the height and angle of twist in a sprag clutch

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.

The Twisting Angle & Impact on the Mating Component

The mating components don’t lock up instantaneously the moment the call to transmit torque is made. While the sprags are rotating to reach the equilibrium point, the mating components are also rotating relative to each other, but this time in the torque transmission direction, not the freewheel direction.

The amount these mating components rotate until the sprags reach equilibrium is called the twisting angle, or angle of twist.

The twisting angle is very small and is typically under 3° for nominal torque values, but if the torque is small that twisting angle can be close to 0. However, relative to other clutch mechanisms, even 3° is considered quite small.

For applications where precise twisting angle is needed, the value can be calculated based on application gap heights, mating surface hardness, and application torque.

To learn more about angle of twist and our sprag clutches, contact GMN Bearing USA today!

Interested in GMN Sprag Clutches?

Check out our Sprag Clutch Guide resources below for more information.

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