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The purpose of a clutch is to initiate motion or increase the velocity of a mass generally by transferring kinetic energy from another moving item. The mass being accelerated is generally a rotating inertial load . Using a friction type clutch the energy is generally transferred using surfaces lined with friction material... Using a positive clutch the energy is transferred using interlocking teeth or projecting lugs. However magnetic force or fluid viscosity is also used to transfer torque

Clutch Type

Clutch type Description Notes
Plate Two types :single disc and multi disc. Discs generally have fabric linings on both sides to transmit torque from adjacent rotating discs when clamping forces are applied. Clamping force may be via springs. Axial Plate
Cone The clutch drives between internal and external cones instead of plates. The clutch is engaged when the inner cone(external) is forced into the outer (internal) cone. The cone clutch utilises the wedging action of the parts to increase the normal force on the lining. Thus an increase in the tangential friction and the torque results. The clutch has improved thermal properties over a plate clutch . Cone Clutch
Eddy Current If a conductor moves relative to magnetic field cutting the lines of magnetic field then rings of currents are induced in the conductor round the lines of the magnetic field.   The induced currents generate magnetic fields opposing the change i.e. try to stop the relative motion.
The eddy current clutch uses this principle by having an input rotating member which drives an output rotating member.   One of the rotating members is a magnet ( permanent or electromagnet)and the other is a conductor. The torque transmitted is related to the intensity of eddy currents which are set by the relative speed using permanent magnets or by adjusting the flux field using electromagnets.
Dog A clutch in which projections on one part fit into recesses on the other part. This is a positive drive clutch. Old fashion design but very simple  
Fluid This type of clutch transfers torque using a viscous fluid in a chamber. This system allows the speed on the driven side to progressively increase up to the speed of the driving side. Not very good for sudden changes of load  
Sprag This is basically an inner race and and outer race and the annulus between is occupied by a number of sprags.   The sprags are steel blocks positioned and shaped such that if they will transmit power from one race to the other by a wedging action in the driving direction.   Rotation in the other direction frees the sprags and the clutch is disengaged. Either race can be the driver. This type of clutch can be used to allow simple over-running, indexing, or back-stopping.  

Links to Clutch Design
  1. Clutches and Brakes ...A detailed selection and design guide download book
  2. Mayr ...Brakes and Clutches
  3. Renold .Sprag Clutches
  4. Emerson.. .. Morse Info on Clutches
  5. Magnetictech .. Eddy Current Clutches
  6. Warner ..Brake /Clutch Information/Data sheets
  7. Twiflex .. Centrifugal Clutch Information/Data sheets- Registration Required
  8. Clutches and Brakes .. A review of the different types of clutches and Brakes
  9. Wichita Clutches & Brakes .. A supplier of Brakes and Clutches with downloadable data sheets

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Last Updated 20/01/2013