Freewheel
（重定向自Overrunning clutch）
![Freewheel mechanism](/Images/godic/202501/31/Freewheel_en.svg1332.png")
![Ratcheting freewheel mechanism (van Anden, 1869)](/Images/godic/202501/31/Roue_libre_cliquet.svg1332.png")
In mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft. An overdrive is sometimes mistakenly called a freewheel, but is otherwise unrelated.