Universalgelenk

Universalgelenk, also known as the universal joint or Cardan joint, is a mechanical linkage used to connect two rotating shafts that are not in line with each other, allowing the transmission of torque and rotary motion while accommodating angular misalignment.

Construction and operation: The joint comprises two yokes connected by a cross-shaped spider with four trunnions. Each yoke is mounted on a shaft; the cross is retained by bearings at the trunnions. As the input shaft turns, the cross drives the second yoke, bending through the angle between the shafts. The joint transmits torque over a range of angles but introduces a variation in output speed.

Kinematics and limitations: The instantaneous angular velocity of the output shaft is not constant when the shafts are angled, except when the angle is small or when two U-joints are used with proper phasing. In automotive drives, this velocity fluctuation is typically accepted or canceled by using a second U-joint arranged to compensate the fluctuation.

Applications: Universalgelenke are widely used in automobile drive shafts, power tools, industrial machinery, and marine transmissions to transmit power between misaligned components. They are chosen for their compactness, ability to transmit torque through angular offset, and relative simplicity.

Variants and maintenance: A single Cardan joint may be used alone; two joints in series (double Cardan) with a correctly oriented intermediate shaft can achieve nearly constant velocity. Proper lubrication and seals are required to minimize wear; misalignment, overloading, or inadequate lubrication reduces service life.