Thompson Coupling
The Thompson constant velocity joint (TCVJ), also known as a Thompson coupling, assembles two cardan joints within each other to eliminate the intermediate shaft. A control yoke is added to keep the input and output shafts aligned. The control yoke uses a spherical pantograph scissor mechanism to bisect the angle between the input and output shafts and to maintain the joints at a relative phase angle of zero. The alignment ensures constant angular velocity at all joint angles. Eliminating the intermediate shaft and keeping the input shafts aligned in the homokinetic plane greatly reduces the induced shear stresses and vibration inherent in double cardan shafts. While the geometric configuration does not maintain constant velocity for the control yoke that aligns the cardan joints, the control yoke has minimal inertia and generates little vibration. Continuous use of a standard Thompson Coupling at a straight-through, zero-degree angle will cause excessive wear and damage to the joint; a minimum offset of 2 degrees between the input and output shafts is needed to reduce control yoke wear. Modifying the input and output yokes so that they are not precisely normal to their respective shafts can alter or eliminate the "disallowed" angles.
The cardan joints within the Thompson Coupling can use roller bearings for all bearing surfaces; this reduces friction and wear when compared to the sliding joints used in Rzeppa-type CV joints.
The novel feature of the coupling is the method for geometrically constraining the pair of cardan joints within the assembly by using, for example, a spherical four bar scissors linkage (spherical pantograph) and it is the first coupling to have this combination of properties.
The coupling earned its inventor, Glenn Thompson, the Australian Society for Engineering in Agriculture Engineering Award.
Read more about this topic: Constant-velocity Joint
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