A universal joint, also known as Hooke’s joint, is used to connect two non-parallel and intersecting shafts or misaligned shafts. A common application is in automobiles, where it transmits power from the gearbox to the rear axle.

Figure 3.14: Hooke’s joint

Construction and Working

Consider a universal joint connecting two horizontal shafts (shaft 1 and shaft 2) at an angle \( \alpha \). The shafts are supported on bearings and each has a fork at its end.

The four ends of the two forks are connected by a central cross-shaped piece. The right-angle arms of this center piece rest in bearings provided in the fork ends of both shafts.

This arrangement allows transmission of rotary motion between misaligned shafts, though the angular velocity of the output shaft is not uniform if the input shaft rotates at constant speed.

Historical Note

Between 1667 and 1675, Robert Hooke analyzed the joint and discovered its non-uniform rotational behavior. The term "universal joint" was first recorded in reference to this device by Hooke himself.