How Does It Work: Overrunning Clutch

If you’ve ever coasted downhill on a bicycle, you’ve enjoyed the benefits of an overrunning clutch.

But an overrunning clutch does more than smooth out a bicycle ride. They make heavy machinery function efficiently and safely. Keep reading to learn about how an overrunning clutch works. 

What is an Overrunning Clutch? 

An overrunning clutch is also known as a freewheel clutch. It is a mechanism that allows the driven shaft to turn freely under specific conditions.

You can find an overrunning clutch in heavy-duty applications as well as bicycles. The agriculture, aerospace, mining, and industrial metal processing industries all benefit from the overrunning clutch. 

How Does an Overrunning Clutch Work? 

When the shaft you’re controlling, the driven shaft, rotates faster than the drive shaft, the overrunning clutch will mechanically disconnect the two shafts. So the driven shaft can keep moving faster without affecting the driven shaft.

The overrunning clutch overruns the process, allowing the driven shaft to spin freely without the driveshaft controlling it. 

This is why a cyclist can keep moving downhill without moving his pedals, making inventions like the e-bike possible. 

Technically, the overrunning clutch transfers torque only in one direction. The overrunning clutch then permits the driven shaft to keep rotating even when you stop the driver. 

Bicycles and Heavy Machinery

You can find an overrunning clutch on more than a bicycle, though. You can find it in just about any mechanical piece of machinery.

The overrunning clutch will connect to coaxial shafts. Sometimes it will connect a shaft to a freely moving part resting on the shaft. 

Not all overrunning clutches look the same. You can find these three configurations:

  • Ratchet and jaw configuration
  • Circular cylinder and eccentric rollers
  • Self-tensioning helical springs

Each of these configurations helps create an overrunning clutch. You can find them in a variable transmission where they convert a rocking motion to a rotary motion.

You will also find them in machines like metal-cutting machines with high-speed shifting. These machines need a slowly rotating shaft to rotate faster in the same direction. Arresting devices and winding mechanisms that need a clutch to prevent reverse shaft rotation also use overriding clutches. 

What is the Purpose of the Overrunning Clutch in the Starter Drive? 

When you attempt to start your heavy machinery, you need the engine to start to turn freely as your engine attempts to run. The overrunning clutch in the starter drive makes this happen. So the overrunning clutch transmits torque in one direction but then freewheels in another direction. 

The starter motor can then transmit torque to the ring gear. This way, the ring gear cannot transfer torque to the starter motor. 

PTO Overrunning Clutch Function 

You may wonder, from 0–10, what does a PTO overrunning clutch do? 

Similarly, the overrunning clutch allows a shaft to freewheel; the overrunning clutch allows a PTO shaft to move in one direction. Thus the overrunning clutch controls the speed of the implement that a tractor is hauling. It prevents the farm implement from going faster than the speed of the tractor when the tractor slows down. 

So, the overrunning clutch accomplishes which of the following? 

  • A vehicle can start. 
  • The implement being hauled cannot run faster than the tractor hauling it. 
  • You can coast downhill on your bicycle. 

If you’ve answered all three, you are correct. 

Critical Element

Because the overriding clutch is critical, you should have your heavy machinery inspected regularly. Overhead cranes and the like need regular maintenance. 

Contact us for all of your parts and mechanical inspection needs.

Posted in Industrial Brakes and Clutches.