A double cardan joint consists of two universal joints mounted back
to back with a center yoke; the center yoke replaces the
intermediate shaft. Provided that the angle between the input shaft
and center yoke is equal to the angle between the center yoke and
the output shaft, the second cardan joint will cancel the velocity
errors introduced by the first cardan joint and the aligned double
cardan joint will act as a CV joint.
Double Cardan joints are similar to double Cardan shafts, except
that the length of the intermediate shaft is shortened leaving only
the yokes; this effectively allows the two Hooke's joints to be
mounted back to back. DCJs are typically used in steering columns,
as they eliminate the need to correctly phase the universal joints
at the ends of the intermediate shaft (IS), which eases packaging
of the IS around the other components in the engine bay of the car.
They are also used to replace Rzeppa style constant-velocity joints
in applications where high articulation angles, or impulsive torque
loads are common, such as the driveshafts and halfshafts of rugged
four wheel drive vehicles. Double Cardan joints require a centering
element that will maintain equal angles between the driven and
driving shafts for true constant velocity rotation. This centering
device requires additional torque to accelerate the internals of
the joint and does generate some additional vibration at higher
speeds.
