Watt's linkage

In kinematics, Watt's linkage (also known as the parallel linkage) is a type of mechanical linkage invented by James Watt in which the central moving point of the linkage is constrained to travel on a nearly straight line. It was described in Watt's patent specification of 1784 for the Watt steam engine.

Today it is used in automobile suspensions, allowing the axle of a vehicle to travel vertically while preventing sideways motion.