One way clutch 

The one-way clutch, or, as it is also often called, overrunning clutch, is a simple mechanism that ensures disconnection of the torque from the driven shaft. This is necessary when the shaft speed increases uncontrollably and begins to exceed a predetermined value. Also, overrunning devices are in demand in cases where there is a need to transfer torque only in one direction. The one-way clutches are used in automotive and mechanical industries in gearboxes, as well as in freewheeling devices of starters and generators. Today the clutches of ratchet and roller design are the most common.