A universal joint, U-joint, Cardan joint, Hardy-Spicer joint, or Hooke's joint is a linkage that transmits rotation between two non parallel shafts whose axes are coplanar but not coinciding., and is commonly used in shafts that transmit rotary motion. It is used in automobiles where it is used to transmit power from the gear box of the engine to the rear axle. The driving shaft rotates at a uniform angular speed, where as the driven shaft rotates at a continuously varying angular speed.
A complete revolution of either shaft will cause the other to rotate through a complete revolution at the same time. Each shaft has fork at its end. The four ends of the two fork are connected by a centre piece, the arms of which rest in bearings, provided in fork ends. The centre piece can be of any shape of a cross, square or sphere having four pins or arms. The four arms are at right angle to each other.
When the two shafts are at an angle other than 180° (straight), the driven shaft does not
rotate with constant angular speed in relation to the drive shaft; the more the angle goes toward 90° the jerkier the movement gets (clearly, when the angle β = 90° the shafts would even lock).
However, the overall average speed of the driven shaft remains the same as that of driving shaft, and so speed ratio of the driven to the driving shaft on average is 1:1 over multiple rotations.
The angular speed ω2 of the driven shaft, as a function of the angular speed of the driving shaft ω1 and the angle of the driving shaft φ1, is found using:
ω2 = ω1 cosα / (1-sin2α.cos2θ)
For a given and set angle between the two shafts it can be seen that there is a cyclical variation in the input to output velocity ratio. Maximum values occur when sin θ = 1, i.e. when θ = 900 and 2700. The denominator is greatest when θ = 0or 1800 and this condition gives the minimum ratio of the velocities.
Components of Hooke’s Joint
Slip Joint in the Propeller Shaft;
Hook Joint in the Propeller Shaft;