Fluid Coupling Overview
A fluid coupling includes three components, plus the hydraulic fluid:
The casing, also called the shell (which will need to have an oil-tight seal around the drive shafts), contains the fluid and turbines.
Two turbines (enthusiast like components):
One linked to the input shaft; known as the pump or impellor, primary steering wheel input turbine
The other connected to the result shaft, known as the turbine, output turbine, secondary steering wheel or runner
The driving turbine, known as the ‘pump’, (or driving torus) is rotated by the prime mover, which is normally an interior combustion engine or electric powered engine. The impellor’s movement imparts both outwards linear and rotational movement to the fluid.
The hydraulic fluid is normally directed by the ‘pump’ whose shape forces the flow in direction of the ‘output turbine’ (or driven torus). Right here, any difference in the angular velocities of ‘input stage’ and ‘output stage’ lead to a net pressure on the ‘result turbine’ leading to a torque; thus leading to it to rotate in the same path as the pump.
The motion of the fluid is efficiently toroidal – going in one direction on paths which can be visualised to be on the surface of a torus:
When there is a notable difference between input and result angular velocities the motion has a element which is normally circular (i.e. round the bands formed by sections of the torus)
If the insight and output stages have identical angular velocities there is absolutely no net centripetal force – and the movement of the fluid is definitely circular and co-axial with the axis of rotation (i.e. round the edges of a torus), there is absolutely no stream of fluid from one turbine to the additional.
An important characteristic of a fluid coupling can be its stall quickness. The stall quickness is defined as the highest speed at which the pump can change when the result turbine is certainly locked and optimum input power is applied. Under stall conditions all of the engine’s power would be dissipated in the fluid coupling as heat, perhaps leading to damage.
A modification to the easy fluid coupling may be the step-circuit coupling that was formerly manufactured as the “STC coupling” by the Fluidrive Engineering Organization.
The STC coupling consists of a reservoir to which some, but not all, of the essential oil gravitates when the output shaft is normally stalled. This decreases the “drag” on the input shaft, resulting in reduced fuel usage when idling and a reduction in the vehicle’s tendency to “creep”.
When the result shaft begins to rotate, the oil is thrown out of the reservoir by centrifugal drive, and returns to the primary body of the coupling, so that normal power transmitting is restored.
A fluid coupling cannot develop result torque when the input and result angular velocities are identical. Hence a fluid coupling cannot achieve completely power transmission efficiency. Because of slippage that will occur in any fluid coupling under load, some power will always be dropped in fluid friction and turbulence, and dissipated as warmth. Like other fluid dynamical gadgets, its efficiency tends to increase steadily with increasing level, as measured by the Reynolds quantity.
As a fluid coupling operates kinetically, low viscosity liquids are preferred. Generally speaking, multi-grade motor oils or automated transmission liquids are used. Raising density of the fluid increases the amount of torque which can be transmitted at confirmed input speed. However, hydraulic fluids, very much like other liquids, are subject to adjustments in viscosity with temp change. This prospects to a switch in transmission overall performance and so where unwanted performance/efficiency change has to be kept to the very least, a motor oil or automatic transmission fluid, with a higher viscosity index should be used.
Fluid couplings can also act as hydrodynamic brakes, dissipating rotational energy as high temperature through frictional forces (both viscous and fluid/container). When a fluid coupling can be used for braking additionally it is referred to as a retarder.
Fluid Coupling Applications
Fluid couplings are used in many commercial application concerning rotational power, especially in machine drives that involve high-inertia begins or continuous cyclic loading.
Fluid couplings are found in some Diesel locomotives as part of the power transmission system. Self-Changing Gears produced semi-automated transmissions for British Rail, and Voith manufacture turbo-transmissions for railcars and diesel multiple products which contain various combinations of fluid couplings and torque converters.
Fluid couplings were found in a variety of early semi-automatic transmissions and automated transmissions. Since the late 1940s, the hydrodynamic torque converter has replaced the fluid coupling in motor vehicle applications.
In motor vehicle applications, the pump typically is connected to the flywheel of the engine-in reality, the coupling’s enclosure could be part of the flywheel correct, and thus is switched by the engine’s crankshaft. The turbine is linked to the insight shaft of the transmitting. While the transmission is in equipment, as engine velocity increases torque is certainly transferred from the engine to the input shaft by the movement of the fluid, propelling the automobile. In this regard, the behavior of the fluid coupling strongly resembles that of a mechanical clutch driving a manual transmitting.
Fluid flywheels, as specific from torque converters, are most widely known for their make use of in Daimler vehicles together with a Wilson pre-selector gearbox. Daimler used these throughout their selection of luxury cars, until switching to automated gearboxes with the 1958 Majestic. Daimler and Alvis were both also known for his or her military automobiles and armored vehicles, a few of which also used the mixture of pre-selector gearbox and fluid flywheel.
The most prominent usage of fluid couplings in aeronautical applications was in the DB 601, DB 603 and DB 605 motors where it had been used as a barometrically managed hydraulic clutch for the centrifugal compressor and the Wright turbo-substance reciprocating engine, where three power recovery turbines extracted approximately 20 percent of the energy or around 500 horsepower (370 kW) from the engine’s exhaust gases and, using three fluid couplings and gearing, converted low-torque high-acceleration turbine rotation to low-speed, high-torque output to operate a vehicle the propeller.