A sprag clutch is primarily an over-running device. It allows one element to be stationary while the other rotates around it. The sprag clutch is needed to let the drive gears spin at motor speed when the engine is running (while the starter gear is stationary). Thus the over-running function.
Note that cam shape of the individual sprags allows lockup when the starter motor is driving the gearing. Sprag clutches are also known as one-way clutches.
A bendix style starter arrangement has the gearing move into engagement while cranking, then it moves back to release when the operator stops using the starter button.
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2011 EC250E
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