Clutch - Other Clutches and Applications

Other Clutches and Applications

• Belt clutch: Used on agricultural equipment and some piston-engine-driven helicopters. Engine power is transmitted via a set of vee-belts that are slack when the engine is idling, but by means of a tensioner pulley can be tightened to increase friction between the belts and the sheaves.
• Dog clutch: Utilized in automobile manual transmissions mentioned above. Positive engagement, non-slip. Typically used where slipping is not acceptable. Partial engagement under any significant load tends to be destructive.
• Hydraulic clutch: The driving and driven members are not in physical contact; coupling is hydrodynamic.
• Electromagnetic clutch: Typically a clutch that is engaged by an electromagnet that is an integral part of the clutch assembly. However, magnetic particle clutches have magnetically influenced particles contained in a chamber between driving and driven members which upon application of direct current causes the particles to clump together and adhere to the operating surfaces. Engagement and slippage are notably smooth.
• Overrunning clutch or freewheel: If some external force makes the driven member rotate faster than the driver, the clutch effectively disengages. Examples include:
  • Borg-Warner overdrive transmissions in cars
  • Ratchet: typical bicycles have these so that the rider can stop pedaling and coast
  • An oscillating member where this clutch can then convert the oscillations into intermittent linear or rotational motion of the complimentary member; others use ratchets with the pawl mounted on a moving member
  • The winding knob of a camera employs a (silent) wrap-spring type as a clutch in winding and as a brake in preventing it from being turned backwards.
  • The rotor drive train in helicopters uses a freewheeling clutch to disengage the rotors from the engine in the event of engine failure, allowing the craft to safely descend by autorotation.
• Wrap-spring clutches: These have a helical spring wound with square-cross-section wire. In simple form the spring is fastened at one end to the driven member; its other end is unattached. The spring fits closely around a cylindrical driving member. If the driving member rotates in the direction that would unwind the spring the spring expands minutely and slips although with some drag. Rotating the driving member the other way makes the spring wrap itself tightly around the driving surface and the clutch locks up.