Fluid coupling

Observe the following figure:

 

 

•The second fan which is not electrically connected also turns along with the first fan

•Air is ‘fluid’ used as the medium of power transfer

•Fluid coupling is a hydrodynamic device which transmit torque solely through dynamic fluid

 action

•Fluid coupling is also termed as liquid coupling, Fluid flywheel

Location of Fluid Coupling:

•Located between engine crank shaft and the

 transmission 

 

 Construction Details:

 •Two half dough nut shaped shells equipped with  interior fins radiate from hubs 

 •One shell (driving member) is fastened to flywheel 

 •Other shell is fastened to transmission shaft

 •The drive and driven members are convex shape steel or aluminum alloy castings having

  directional blades 

 •Housing surrounds both driving and driven members 

 •80 percent of interior of assembly is filled with oil 

 Working of Fluid Coupling:

 •When engine is started, driving member rotate at engine speed 

 •Driving member carries oil in its vanes

 •Because of the shape of the driving member and the centrifugal force the oil is forced to

  flow into the vanes of driven member

 •Flow pattern now established is vortex flow 

 •When engine speed increases more oil is circulated from driving member to driven member

 •As the speed increases vortex flow decreases and changes to rotary flow 

 •Driven member rotates in the same direction as the driving member

 •At the maximum rotary flow the oil molecules form a solid mass and start to clutch both 

   members together 

 •If both speeds were absolutely equal, the assembly would rotate as a unit   

   •Efficiency increases rapidly from zero at rest to nearly 99 

  percent at high speeds 

 

 Advantages of Fluid Coupling:

 •Drive is taken up smoothly 

 •Enables the driver to use clutch and gears with less skill and 

  fatigue 

 •Fluid absorbs transmission shocks

 •Coupling prevents stalling the engine even if driver fails to de-clutch or shift to gear 

  position into neutral 

 •Vehicle may be started in any gears 

 Disadvantages of Fluid Couplin:

 •At low speeds it is not efficient as mechanical ones 

 • Not suited for use with an ordinary gearbox