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Unlike some other coupling types, it is not intended to compensate for mis-alignment between shafts. The coupling may have a small ability to compensate for varying alignment, but if this is needed it is generally done through using an additional coupling in tandem. The coupling also runs at the same speed for input and output shafts, unlike a torque converter.
Geislinger couplings are constructed inside robust enclosed steel housings. An outer housing and a central hub or "inner star" form the input and output drive members. Internally, the drive is transmitted through a number of radial leaf springs. The steel leaf springs are arranged as multi-leaf tapered packs, so that their stiffness increases progressively with displacement. These leaf springs are housed in triangular spaces within the outer housing, the tips of the longest leaves engaging in splines in the inner star.
Viscous damping is provided, as the leaf springs are immersed in oil. Any movement of the spring plates must squeeze oil through the narrow gaps around them between the plates and the casing. As the springs have a high surface area, yet there is only a small gap between them and their housing, the damping factor can be high. The oil used for damping is usually supplied by the engine lubrication system, through a drilling in the crankshaft. If this is unavailable, an oil-filled coupling can be used. This oil filling also aids lubrication and encourages a long service life.
The coupling is mostly used on the output of large diesel engines. It isolates vibration between engines, shafts and loads. A major benefit can be to avoid resonance problems where systems have a critical speed that must be avoided. Use of a damped coupling can shift this frequency to an unimportant speed, broaden the peak of the resonance to make it less severe, or even damp it out altogether. The Geislinger coupling's ability to easily tailor its damping is valuable here to allow tuning for a particular frequency.
A related device is the Geislinger damper. This is broadly the same coupling, but both input and output shafts are connected to the same central hub. The massive outer casing is connected to this through similar leaf spring packs, but is free to move torsionally, with damping. It is used as a harmonic damper to control vibrations in shafts.
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