Fluid Coupling - Overview

Overview

A fluid coupling consists of three components, plus the hydraulic fluid:

• The housing, also known as the shell (which must have an oil tight seal around the drive shafts), contains the fluid and turbines.
• Two turbines (fan like components):
  • One connected to the input shaft; known as the pump or impellor, primary wheel input turbine
  • The other connected to the output shaft, known as the turbine, output turbine, secondary wheel or runner

The driving turbine, known as the 'pump', (or driving torus) is rotated by the prime mover, which is typically an internal combustion engine or electric motor. The impellor's motion imparts both outwards linear and rotational motion to the fluid.

The hydraulic fluid is directed by the 'pump' whose shape forces the flow in the direction of the 'output turbine' (or driven torus). Here, any difference in the angular velocities of 'input stage' and 'output stage' result in a net force on the 'output turbine' causing a torque; thus causing it to rotate in the same direction as the pump.

The motion of the fluid is effectively toroidal - travelling in one direction on paths that can be visualised as being on the surface of a torus:

• If there is a difference between input and output angular velocities the motion has a component which is circular (i.e. round the rings formed by sections of the torus)
• If the input and output stages have identical angular velocities there is no net centripetal force - and the motion of the fluid is circular and co-axial with the axis of rotation (i.e. round the edges of a torus), there is no flow of fluid from one turbine to the other.