NEW VERSION with improved video & sound: https://www.youtube.com/watch?v=YKHeqHMye4k more at http://auto-parts.quickfound.net/ "DEMONSTRATION OF FLUID COUPLING WITH THE USE OF A PLASTIC MODEL IN OPERATION AND A TRUCK IN ACTION." Public domain film from the National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied. The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and equalization. http://en.wikipedia.org/wiki/Fluid_coupling A fluid coupling is a hydrodynamic device used to transmit rotating mechanical power. It has been used in automobile transmissions as an alternative to a mechanical clutch. It also has widespread application in marine and industrial machine drives, where variable speed operation and/or controlled start-up without shock loading of the power transmission system is essential. History The fluid coupling originates from the work of Dr. Hermann Föttinger, who was the chief designer at the AG Vulcan Works in Stettin. His patents from 1905 covered both fluid couplings and torque converters. In 1930 Harold Sinclair, working with the Daimler company, devised a transmission system using a fluid coupling and planetary gearing for buses in an attempt to mitigate the lurching he had experienced while riding on London buses during the 1920s. In 1939 General Motors Corporation introduced Hydramatic drive, the first fully automatic automotive transmission system installed in a mass produced automobile. The Hydramatic employed a fluid coupling. The first Diesel locomotives using fluid couplings were also produced in the 1930s. 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[note 1]) 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[note 1]). 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. Stall speed An important characteristic of a fluid coupling is its stall speed. The stall speed is defined as the highest speed at which the pump can turn when the output turbine is locked and maximum input power is applied. Under stall conditions all of the engine's power would be dissipated in the fluid coupling as heat, possibly leading to damage. Step-circuit coupling A modification to the simple fluid coupling is the step-circuit coupling which was formerly manufactured as the "STC coupling" by the Fluidrive Engineering Company. The STC coupling contains a reservoir to which some, but not all, of the oil gravitates when the output shaft is stalled. This reduces the "drag" on the input shaft, resulting in reduced fuel consumption when idling and a reduction in the vehicle's tendency to "creep". When the output shaft begins to rotate, the oil is thrown out of the reservoir by centrifugal force, and returns to the main body of the coupling, so that normal power transmission is restored. Slip A fluid coupling cannot develop output torque when the input and output angular velocities are identical. Hence a fluid coupling cannot achieve 100 percent power transmission efficiency. Due to slippage that will occur in any fluid coupling under load, some power will always be lost in fluid friction and turbulence, and dissipated as heat. The very best efficiency a fluid coupling can achieve is 94 percent, that is for every 100 revolutions input, there will be 94 revolutions output. Like other fluid dynamical devices, its efficiency tends to increase gradually with increasing scale, as measured by the Reynolds number...